Light emitting diode, optical semiconductor element and epoxy resin composition suitable for optical semiconductor element and production methods therefor

ABSTRACT

A light emitting diode comprising an LED chip having a light emitting layer made of a nitride compound semiconductor and a light transmitting resin that includes a fluorescent material which absorbs at least a part of light emitted by the LED chip and emits light of a different wavelength, wherein the fluorescent material includes a fluorescent particles of small particle size and a fluorescent particles of large particle size, the fluorescent particles of large particle size being distributed in the vicinity of the LED chip in the light transmitting resin to form a wavelength converting layer, the fluorescent particles of small particle size being distributed on the outside of the wavelength converting layer in the light transmitting resin.

TECHNICAL FIELD

The present invention relates to an optical semiconductor device such aslight emitting diode of mainly surface mounted type that can be used forthe back light of a liquid crystal display, full-color display, built-inlamp of a switch, illumination light source, various indicators andtraffic lights, and a method for producing the same, and a lighttransmitting epoxy resin composition that has high light resistance andpliability suitable for the light emitting diode.

BACKGROUND ART

An LED chip that uses a nitride semiconductor (In_(X)Ga_(Y)Al_(1−X−Y)N,0≦X≦1, 0≦Y≦1), a semiconductor light emitting element capable ofemitting blue light with high brightness has recently been developed.Light emitting devices based on nitride semiconductor have suchadvantages as higher output power than those of light emitting devicesthat use GaAs, AlInGaP or the like to emit light within a range from redto yellowish green and less color shift caused by temperature change,but has such a drawback that it is difficult to obtain a high outputpower in a wavelength region including the wavelength of green light andlonger. On the other hand, the applicant of the present invention havedeveloped a light emitting diode that is capable of emitting white lightby disposing YAG:Ce fluorescent material, a fluorescent material capableof absorbing a part of blue light emitted by the LED chip describedabove thereby emitting yellow light, on the LED chip and have appliedfor patent (International Publication No. WO98/5078).

The light emitting diode is, despite the relatively simple constitutionof single-chip two-terminal configuration, capable of synthesizing lightfrom the LED chip that is electrically connected to a lead electrode andlight from a fluorescent material such as YAG:Ce included in a lighttransmitting resin that covers the LED chip, and emitting thesynthesized white light through a convex lens.

The light emitting diode allows it to modify the synthesized lightemitted by the light emitting diode from bluish white to a desired colorsuch as yellowish white by adjusting the content of the fluorescentmaterial. It may also be possible to emit yellow or red light, forexample, by adding a pigment.

Meanwhile diversification of the applications for the light emittingdiode has generated the needs for a light emitting diode that can emitlight with higher luminance.

In recent years, chip light emitting diodes are widely used as the lightsource for illuminating switch, full-color display, back light forliquid crystal display and the like. The chip light emitting diode ismade by electrically connecting a light emitting element in a recess ofa package and covering the light emitting element with a lighttransmitting resin so as to seal the chip.

On the other hand, the rapid advancement in the optical semiconductortechnology has been causing a great increase in the output power of theoptical semiconductor devices and remarkable decrease in the wavelengthof the emitted light. A light emitting diode made of a nitridesemiconductor, for example, can emit light with peak intensity at anywavelength within a range from about 350 nm to 650 nm depending on theelements that constitute the light emitting layer. It has also be madepossible to emit light with a high output power of 5 mW or over invisible light region of wavelengths not longer than 550 nm (includingnear ultraviolet and blue-green light) by using multiple quantum wellstructure in the light emitting layer of a nitride semiconductor. Such ahigh output power gives rise to a new problem. That is, for a opticalsemiconductor device that can emit or receive light of such a highenergy, it is important to prevent the molding resin from beingdeteriorated by the light and reduce the stress generated by heatbetween the molding resin and the optical semiconductor chip.

Japanese Unexamined Patent Publication No. 2000-196151 discloses amolding resin containing, as a main component, an alicyclic epoxy resininstead of bisphenol epoxy resin. An epoxy resin composition obtained bycuring the alicyclic epoxy resin, as a main component, with an acidanhydride contains substantially no carbon-carbon double bond, thatcauses light deterioration, in a main skeleton thereof. As a result,such an epoxy resin composition is less susceptible to deterioration ofthe molding resin even after being irradiated with light for a longperiod of time and has relatively good pliability. Thus thesemiconductor chip is less likely to be damaged by the thermal stress.

However, epoxy resin cured by acid anhydride cannot be used in a surfacemounted device (SMD) that comprises a semiconductor chip mounteddirectly on the substrate surface, since such a device requires it toform a thin film of the molding resin. That is, the surface mounteddevice requires a thin film of the molding resin 1 mm or less inthickness formed thereon, the mixture liquid of epoxy resin that isapplied has a larger area exposed to the atmosphere. However, since theacid anhydride curing agent has high volatility and high hydroscopicityand takes a relatively longer time, from 5 to 20 hours, to cure, theacid anhydride curing agent absorbs moisture and evaporates duringcuring, thus making it difficult for the epoxy resin to properly cure.The epoxy resin that has cured unsatisfactorily cannot demonstrate theproper function of resin with the light and heat resistancesignificantly deteriorated.

For the reason described above, a cation-curing agent such as aromaticsulfonium salt is commonly used instead of the acid anhydride curingagent for such applications that require thin film such as surfacemounted device. The cation curing agent allows for satisfactory curingeven when a mixture liquid thereof with epoxy resin is applied in a thinfilm, because of low volatility.

However, since the cation curing agent has an intrinsic tendency toabsorb blue light and light having shorter wavelengths, epoxy resin thathas been cured by the cation curing agent is liable to discoloration,namely to become yellowish due to absorption of short wavelength light.As a result, it has been difficult to use epoxy resin that is cured bythe cation curing agent in a optical semiconductor device that emits orreceives blue light and shorter wavelengths. Also because the curingreaction proceeds almost only by the ring-opening reaction of epoxygroups, the epoxy resin composition thus obtained has athree-dimensional network wherein ether bonds are arranged relativelyorderly and has lower pliability. Thus there has been such a problem,when epoxy resin that is cured by means of a cation curing agent is usedin a optical semiconductor device, that a large stress is generatedbetween the optical semiconductor chip and the molding resin duringheating and cooling of the optical semiconductor device, eventuallyleading to cracks generated in the optical semiconductor chip and wirebreakage.

To improve the pliability of epoxy resin composition cured with thecation curing agent, the epoxy resin may be mixed with a low-molecularweight reactive diluent such as monoglycidyl ether, polyglycol glycidylether, tertiary carboxyl acid monoglycidyl ether. However, since such areactive diluent impedes curing of the epoxy resin, it becomes necessaryto increase the amount of the cation curing agent added, whichaggravates the problem of yellowing of the epoxy resin composition.

DISCLOSURE OF INVENTION

The present invention has been made to meet the various requirements forthe light emitting diode made of a nitride semiconductor as describedabove.

First, an object of the present invention is to provide a wavelengthconverting light emitting diode that has better light emissioncharacteristic.

Second, an object of the present invention is to provide a method forproducing the light emitting diode having good mass-producingperformance.

Third, an object of the present invention is to provide an epoxy resincomposition that is less susceptible to yellowing and has highpliability while being cured by a cation curing agent, and provide alight emitting diode having excellent light resistance and heatresistance by using such an epoxy resin composition as described aboveas a molding resin.

In order to achieve the objects described above, a first light emittingdiode of the present invention comprises an LED chip having a lightemitting layer formed from a nitride compound semiconductor and a lighttransmitting resin that includes a fluorescent material which absorbs atleast a part of light emitted by the LED chip and emits light of adifferent wavelength.

The fluorescent material includes a fluorescent particles of smallparticle size and a fluorescent particles of large particle size, withthe fluorescent particles of large particle size being distributed inthe vicinity of the LED chip in the light transmitting resin thereby toform a wavelength converting layer, and the fluorescent particles ofsmall particle size being distributed on the outside of the wavelengthconverting layer in the light transmitting resin.

In the first light emitting diode having such a constitution asdescribed above, the wavelength converting layer made of the fluorescentparticles of large particle size can change the light color efficientlywhile the fluorescent particles of small particle size dispersed in anarea surrounding thereof suppresses irregular color.

In the first light emitting diode of the present invention, thefluorescent particles of large particle size is preferably prepared bycontrolling the particle size thereof within a range from 10 to 60 μm,which makes it possible to distribute the fluorescent particles of largeparticle size relatively sparsely in the vicinity of the LED chip in thelight transmitting resin thereby to have the wavelength convertingfunction performed efficiently.

In the first light emitting diode of the present invention, thefluorescent particles of small particle size is preferably prepared bycontrolling the particle size thereof within a range from 0.2 to 1.5 μm,which makes it possible to prevent the fluorescent particles of smallparticle size from precipitating and have the light scattering functionperformed effectively, thus suppressing irregular color moreeffectively.

It is also preferable that the peak diameter of the particle sizedistribution of the fluorescent particles of large particle size iswithin a range from 20 to 90 times the peak diameter of the particlesize distribution of the fluorescent particles of small particle size,which improves the efficiency of light extraction.

A second light emitting diode of the present invention comprises a lightemitting element formed from a semiconductor and a light transmittingresin that includes a fluorescent material which absorbs at least a partof light emitted by the light emitting element and emits light of adifferent wavelength, wherein the fluorescent material is characterizedby a volume-based particle size distribution curve that is flat in aregion of cumulative percentage from 0.01 to 10 vol %. This constitutionmakes it possible to obtain a light emitting diode of high luminance andhigh output power.

In the second light emitting diode of the present invention, it ispreferable that the fluorescent material consists of the fluorescentparticles of small particle size and the fluorescent particles of largeparticle size separated by the flat region described above, while thepeak diameter of the particle size distribution of the fluorescentparticles of large particle size is within a range from 20 to 90 timesthe peak diameter of the particle size distribution of the fluorescentparticles of small particle size, which results in a light emittingdiode having high efficiency of light extraction.

In the first and second light emitting diodes of the present invention,median diameter of the particle size distribution of the fluorescentmaterial is preferably within a range from 15 to 50 μm, which allows itto improve the efficiency of light emission and achieve a light emittingdiode of high luminance. It is also made possible to suppress theformation of dense precipitation that may affect the opticalcharacteristic.

In the first and second light emitting diodes of the present invention,when the distribution frequency of the median diameter of the particlesize distribution is in a region from 20 to 50%, light emission of goodcontrast with suppressed irregular color can be achieved due to lessvariation in the particle size.

Further in the first and second light emitting diodes of the presentinvention, it is preferable to include a diffusing agent along with thefluorescent material in the light transmitting resin, which makes itpossible to achieve uniform light emission with the irregular color evenmore suppressed.

Further in the first and second light emitting diodes of the presentinvention, the light emitting surface of the light transmitting resin ispreferably a curved surface. With this configuration, light emitted bythe light emitting element is scattered in the interface between thelight transmitting resin and the atmospheric air when being extractedthrough the light transmitting resin to the outside, thus making itpossible to suppress the irregular color that tends to occur when thefluorescent particles of large particle size is used. The efficiency oflight extraction at the light emitting surface can also be improved thusallowing to emit light with a higher output power.

A third light emitting diode of the present invention has a package thatcomprises a metal base consisting of a pair of thin metal sheets thatconstitute positive and negative electrodes being joined via a resininsulator for electrical isolation from each other and a side wallbonded to the circumference of the metal base on one side thereofthereby forming a mounting area, an LED chip mounted on the mountingarea and a light transmitting resin that fills the mounting area so asto seal the LED chip.

The light transmitting resin is formed continuously from the mountingarea over the top of the surrounding side wall, while the top surface oflight transmitting resin is flat and substantially parallel to the metalbase and the side face on the circumference of the light transmittingresin is substantially flush with the circumferential side face of thepackage.

The third light emitting diode having such a constitution as describedabove makes it possible to provide a light emitting diode that has highreliability and is suited to mass production. Since the lighttransmitting resin is formed continuously from the mounting area to thetop surface of the side wall, the light emitting surface is expanded tothe entire top surface of the light emitting diode, thus achieving goodbeam directivity.

The light transmitting resin may also include a filler, that may be afluorescent material capable of absorbing a part of light emitted by thelight emitting element and emitting light of a different wavelength.

Although adding a fluorescent material tends to cause irregular color,the constitution of the present invention makes a better light emittingsurface that suppresses irregular color.

Median diameter of the particle size distribution of the fluorescentmaterial is preferably within a range from 15 to 50 μm, and morepreferably within a range from 20 to 50 μm. Using the fluorescentmaterial having such particle sizes allows the wavelength convertingfunction of the fluorescent material to be performed effectively, anddicing process to be carried out satisfactorily thereby improving theyield of production.

A method for producing the light emitting diode according to the presentinvention is a method for producing the third light emitting diode,comprising a first step of making a package assembly consisting of aplurality of packages by bonding an insulating substrate having aplurality of through holes that are grouped corresponding to themounting areas, and a metal base plate having portions separated by theresin insulator in correspondence to the through holes; a second step ofmounting the LED chip in the mounting area of each package formed withthe through hole; a third step of applying and curing the lighttransmitting resin on the top surface of the insulating substrate and inthe through holes by mimeograph printing by using a mask that has anaperture in correspondence to each group; and a fourth step of dividingthe package assembly having the light transmitting resin applied thereoninto individual packages.

This constitution makes it possible to satisfactorily mass-produce thelight emitting diodes that have uniform thickness and flat lightemitting surface and end surface.

According to the producing method of the present invention, themimeograph printing is preferably carried out while repeating the cycleof decreasing and increasing the pressure. This makes it very easy toremove bubbles so that the light emitting diodes that have lessvariations in the characteristics, less unevenness in light emission andless irregular color can be manufactured.

In case the light transmitting resin contains inorganic fillers, inparticular, air tends to be entrapped in the resin so as to form bubblestherein during mixing. Also the optical path length becomes longer whichalso tends to cause irregular color due to a difference in the specificgravity between the fillers and between the filler and the lighttransmitting resin, but the irregular color can be suppressed by theproducing method of the present invention. Thus the light emittingdiodes having variations in the light color and high reliability can bemanufactured.

The epoxy resin composition of the present invention comprises an epoxyresin containing an alicyclic epoxy resin, which accounts for 65% byweight or more of the epoxy resin, an acid anhydride represented by thegeneral formula (1) or dicarboxylic acid represented by the generalformula (2) in an amount of 0.005 to 1.5 mol based on an epoxyequivalent of the epoxy resin, and a cation curing agent in an amount of0.005 to 1.5 mol based on an epoxy equivalent of the epoxy resin.

wherein R₁ represents a cyclic or aliphatic alkyl or aryl having 0 to 12carbon atoms and R₂ represents an alkyl or aryl having 0 to 12 carbonatoms.

The epoxy resin composition of the present invention can be cured byusing the cation curing agent in the amount 1/10 to 1/100 times as muchas that in the prior art because the alicyclic epoxy resin reacts withthe acid anhydride or dicarboxylic acid (hereinafter referred to as anacid anhydride or the like) to form a crosslinked oligomer having somepolymerization degree. Therefore, absorption of light having a shortwavelength caused by the cationic curing agent is inhibited, thus makingit possible to prevent yellowing of the resulting epoxy resincomposition. The epoxy resin composition of the present invention hasnot only an ether bond due to the ring-opening reaction of epoxy groups,but also an ester bond due to the crosslinking reaction between thealicyclic epoxy resin and the acid anhydride or the like so that it hasa three-dimensional network formed by irregular connection of epoxyresins. Therefore, the epoxy resin composition has high pliability evenif a reactive diluent is not used and the use of the epoxy resincomposition in a molding resin of an optical semiconductor devicereduces the thermal stress produced between an optical semiconductorchip and a molding resin, thus making it possible to prevent problemssuch as crack and wire breakage.

The pliability of the epoxy resin composition obtained by the reactionbetween the epoxy resin and the acid anhydride or the like tends to beproportion to the molecular weight of the crosslinked oligomer. Thehigher the proportion of carboxyl groups, which are converted into anester as a result of the reaction with the epoxy resin or a promotordescribed hereinafter, among carboxyl groups of the acid anhydride orthe like in the crosslinked oligomer, the better the pliability of theresulting epoxy resin composition. The reason is considered as follows.As the ester conversion proceeds, volatilization of the acid anhydridein the thin film is less likely to occur in case of curing. The esterconversion ratio of carboxyl groups of the acid anhydride or the like inthe crosslinked oligomer is 10% or more, and preferably 70% or more. Theester conversion ratio can be controlled by the reaction temperature andtime.

The epoxy resin composition of the present invention has an advantagethat, after reacting an alicyclic epoxy resin and an acid anhydride ordicarboxylic acid to obtain a crosslinked oligomer, a mixture of thecrosslinked oligomer and the cation curing agent can be cured. When thealicyclic epoxy resin and acid anhydride or the like are previouslyreacted in a proper reaction vessel to form a crosslinked oligomer and amixture of the crosslinked copolymer and a cation curing agent is moldedover the surface of a substrate of an optical semiconductor device,volatilization of the acid anhydride can be prevented during the curingreaction even in case of molding in the form of a thin film. Since theviscosity of the mixture of the crosslinked copolymer and the cationcuring agent can be freely controlled by the amount of the acidanhydride or the like and the ester conversion ratio, the viscositysuited for handling can be easily set. The mixture of the crosslinkedcopolymer and the cation curing agent has already been polymerized tosome degree, thus resulting in less change in viscosity with a lapse oftime and long pot life.

When using the epoxy resin composition of the present invention in amolding resin of an optical semiconductor device, functional particlessuch as fillers, fluorescent agent particles, diffusing agent particlesand colorant agent particles can be appropriately mixed. Since the mixedsolution of the crosslinked copolymer and the cation curing agent has acomparatively high viscosity, these functional particles are superior indispersibility. Therefore, a desired function can be exhibited in asmall content of the particles, thereby making it possible to reduce aloss in light emission or light reception of the optical semiconductordevice due to light scattering and screening of the functionalparticles.

As the alicyclic epoxy resin in the epoxy resin composition of thepresent invention, for example, epoxidated cyclohexene derivative,hydrated hisphenol A diglycidyl ether and diglycidyl hexahydrophthalateester are preferably used. The use of the alicyclic epoxy resin makes itpossible to obtain an epoxy resin composition which is less likely tocause light deterioration and is superior in pliability.

As the cation curing agent in the epoxy resin composition of the presentinvention, for example, aromatic sulfonium salt, aromatic diazoniumsalt, aromatic iodonium salt and aromatic selenium salt can bepreferably used. These cation curing agents can achieve sufficientcuring in a small amount because of its fast curing rate.

Preferably, the epoxy resin composition of the present invention furthercontains a polyhydric alcohol or a polycondensate thereof in the amountof 0.1 to 5.0 equivalents based on the acid anhydride or dicarboxylicacid. Examples of the usable polyhydric alcohol include ethylene glycol,diethylene glycol, trimethylene glycol, triethylene glycol, propyleneglycol, 1,4-butanediol, and 1,6-hexanediol. The pliability of theresulting epoxy resin composition can be further improved by addingthese polyhydric alcohol or polycondensates thereof.

An optical semiconductor device of the present invention comprises atleast a pair of lead electrodes, an optical semiconductor chip that iselectrically connected to the lead electrodes and a molding resin thatseals the optical semiconductor chip, wherein the epoxy resincomposition of the present invention is used as the molding resin. Thisconstitution makes it possible to manufacture the light emitting diodethat is subject to less decrease in the light emission or receptionefficiency due to yellowing of the molding resin and is less susceptibleto damage to the chip due to thermal cycle and to wire breakage.

The effects of improving the light resistance and the heat resistancecan be achieved remarkably particularly in case the opticalsemiconductor device of the present invention is of the surface mountedtype made by joining the optical semiconductor chip on the surface of asubstrate having lead electrodes formed thereon, or a light emittingdiode chip comprising an optical semiconductor that has a light emittinglayer made of a nitride semiconductor that includes at least In and Gaand a main peak of emission at a wavelength of 550 nm or shorter.

A first method for producing the fluorescent particles of the presentinvention is a method for producing the fluorescent material by firing amixture of a stock material and a flux, wherein the firing processincludes a first firing process of firing in a first reducing atmosphereand a second firing process of firing in a second reducing atmosphere,while the first reducing atmosphere has weaker reducing power than thesecond reducing atmosphere.

The fluorescent material that can absorb the excitation light moreefficiently by producing the fluorescent material by this method.

In the first method for producing the fluorescent material of thepresent invention, aluminum fluoride can be used as the flux.

In the first method for producing the fluorescent material of thepresent invention, a substance including barium fluoride and boric acidcan be used as the flux in which case it is preferable that the fluxincludes a liquid.

When a substance including barium fluoride and boric acid with a liquidadded, thereto is used as the flux, variation in the chromaticity of theemitted light can be suppressed.

A second method for producing the fluorescent material of the presentinvention is a method for producing the fluorescent material by firing amixture of a stock material and a flux, wherein the flux includes bariumfluoride, boric acid and a liquid.

This method can suppress the variation in the chromaticity of the lightemitted from the fluorescent material manufactured thereby.

According to the producing method, water can be used as the liquid.

According to the producing method, Y₂O₃, Gd₂O₃, Al₂O₃ and CeO₂ can beused.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic sectional view of an SMD type light emitting diodeaccording to first embodiment of the present invention.

FIG. 2A is a graph showing the volume-based distribution curve(cumulative percentage of particle sizes) of the fluorescent material ofthe first embodiment.

FIG. 2B is a graph showing the volume-based distribution curve(distribution frequency of particle sizes) of the fluorescent materialof the first embodiment.

FIG. 3A is a schematic plan view of a mask used in mimeograph printingin the producing method of the first embodiment.

FIG. 3B is a schematic plan view showing an enlarged portion of the maskshown in FIG. 3A.

FIG. 4A through FIG. 4D are process diagrams of the mimeograph printingin the producing method of the first embodiment.

FIG. 5 is a sectional view showing a part of a package assembly aftercuring of a light transmitting resin applied by the mimeograph printingin the producing method of the first embodiment.

FIG. 6 is a schematic sectional view of an SMD type light emitting diodeaccording to second embodiment of the present invention.

FIG. 7A and FIG. 7B are sectional views showing processes of forming alight transmitting resin of a light emitting diode Example 5.

FIG. 8 is a schematic sectional view of an SMD type light emitting diodeaccording to Example 1 of the present invention.

FIG. 9A is a graph showing the volume-based distribution curve(cumulative frequency distribution of particle size) of the fluorescentmaterial of Comparative Example 1.

FIG. 9B is a graph showing the volume-based distribution curve(distribution of particle size) of the fluorescent material ofComparative Example 1.

FIG. 10A is a schematic sectional view of a lamp type light emittingdiode according to Example 9 of the present invention.

FIG. 10B is an enlarged view of a portion in the dashed circle in FIG.10A.

FIG. 11A is a graph showing light transmission ratio of epoxy resincomposition before light resistance test.

FIG. 11B is a graph showing light transmission ratio of epoxy resincomposition after light resistance test.

FIG. 12A is a graph showing light transmission ratio of epoxy resincomposition before thermal stability test.

FIG. 12B is a graph showing light transmission ratio of epoxy resincomposition after thermal stability test.

FIG. 13 is a graph showing the variation in the output intensity of alight emitting diode using epoxy resin composition as the molding resin,measured in service life test at a normal temperature.

FIG. 14 is a graph showing the variation in the output intensity of alight emitting diode using epoxy resin composition as the molding resin,measured in a high temperature and high humidity life test.

FIG. 15 is a graph showing the variation in the viscosity of epoxy resincomposition with time.

BEST MODE FOR CARRYING OUT THE INVENTION

Now preferred embodiments of the present invention will be describedbelow with reference to the accompanying drawings.

Embodiment 1

A light emitting diode of the first embodiment is of surface mountedtype (SMD) comprising a light emitting diode chip (LED chip) 5 sealed ina package with a light transmitting resin 8 as shown in FIG. 1. In thelight emitting diode of the first embodiment, the package comprises ametal base 2 and a side wall 1, the side wall 1 being bonded with thecircumference on one side of the metal base 2 for making a mounting area1 a. The LED chip 5 is die-bonded in the mounting area 1 a of thepackage and is, after wiring is made by wire bonding, sealed with thelight transmitting resin 8 (for example, about 1 mm thick over the LEDchip).

In the light emitting diode of the present invention, the epoxy resinproprietary to the present application is used as the sealing resin 8,and the sealing resin includes a fluorescent material (fluorescentmaterial particles) dispersed therein that converts the light emitted bythe light emitting diode (LED) chip into light of different wavelengthand emits this light, thus providing the following features.

First, light resistance and heat resistance are improved by using thelight transmitting sealing resin 8 comprising the epoxy resincomposition that can be cured with a smaller amount of the cation curingagent because crosslinked oligomer is formed through the reaction ofalicyclic epoxy resin and acid anhydride or dicarboxylic acid.

Second, output power and luminance of light emission are greatlyimproved by controlling the particle sizes of the fluorescent material(wavelength converting substance) that is dispersed in the lighttransmitting resin in the specific particle size distribution of thepresent invention.

Now the constitution the light emitting diode of the first embodimentwill be described in detail below.

<Package>

According to this embodiment, the metal base 2 of the package is made ofa thin metal sheet 2 a constituting a positive terminal and a thin metalsheet 2 b constituting a negative terminal that are bonded to each otherwith an insulating resin 4 and connected to a positive electrode 5 a anda negative electrode 5 b of the LED chip 5, respectively, with wires 7.

In the first embodiment, the LED chip 5 is die-bonded with a die bondingresin 6 onto the thin metal film 2 b. According to the presentinvention, however, the LED chip 5 may also be die-bonded onto the otherthin metal film 2 a, or over both the thin metal film 2 a and the thinmetal film 2 b.

<LED chip 5>

Since the light emitting diode of the first embodiment is constituted soas to convert the wavelength of a part or all of the light emitted bythe LED chip 5, the LED chip 5 is made in such a constitution that emitslight of wavelength that can excite the fluorescent material. Whilevarious semiconductors such as ZnSe and GaN can be used for the LED chip5, according to the present invention the LED chip 5 preferably uses anitride semiconductor (In_(X)Al_(Y)Ga_(1−X−Y)N, 0≦X, 0≦Y, X+Y≦1) capableof emitting light of short. wavelength that can efficiently excite thefluorescent material. The LED chip 5 has the light emitting layer madeof In_(X)Ga_(1−X)N (0<X<1), wherein wavelength of the emitted light canbe changed within a range from about 365 nm to 650 nm by changing themixed crystal composition. While the LED chip 5 may be constituted ineither homojunction structure, heterojunction structure or doubleheterojunction structure that has MIS junction, PIN junction or pnjunction according to the present invention, it is preferable to employdouble heterojunction structure that allows light emission with higherluminance. Wide selection of the wavelengths of light emission is madepossible by controlling the chemical composition and mixed crystalcomposition of the semiconductor that constitutes the light emissionlayer (active layer). The active layer may also be made either in singlequantum well structure or multiple quantum well structure including athin film that includes quantum effect.

When the LED chip 5 uses a nitride semiconductor, sapphire, spinel, SiC,Si, ZnO or the like can be used for the substrate, but it is preferableto use a sapphire substrate in order to form the nitride semiconductorof good crystallinity satisfactorily in mass production. The nitridesemiconductor can be formed on the sapphire substrate by MOCVD processor the like. It is preferable to form a buffer layer such as GaN, AlN orGaAlN on the sapphire substrate and form the nitride semiconductor layerhaving pn junction thereon.

The LED chip having pn junction made of nitride semiconductor may bemade in double heterojunction structure by forming the buffer layer onthe sapphire substrate and forming, on the buffer layer, a first contactlayer of n-type gallium nitride, a first cladding layer of n-typealuminum gallium nitride, an active layer of indium gallium nitride, asecond cladding layer of p-type aluminum gallium nitride and a secondcontact layer of p-type gallium nitride successively in the order.

While the nitride semiconductor shows n-type conductivity when not dopedwith an impurity, Si, Ge, Se, Te, C or the like is preferably introducedas an n-type dopant in order to form the desired n-type nitridesemiconductor and Zn, Mg, Be, Ca, Sr, Ba or the like is preferably addedas a p-type dopant in order to form the p-type nitride semiconductor.Since it is difficult to turn the nitride semiconductor into p-typesimply by doping with a p-type dopant, it is preferable to decreaseresistance by heating in a furnace, by plasma irradiation or the likeafter introducing the p-type dopant. Thus the LED chip 5 using thenitride semiconductor can be manufactured by forming the nitridesemiconductor layers and then cutting a wafer having electrodes formedat predetermined positions into individual chips.

In order to have the light emitting diode of the first embodiment emitwhite light, it is preferable to set the wavelength of light emitted bythe LED chip 5 within a range from 400 nm to 530 nm in consideration ofthe relationship of complementary color with the light emitted by thefluorescent material and the need to prevent the light transmittingresin from being deteriorating, and the wavelength is more preferablyset within a range from 420 nm to 490 nm. In order to improve theefficiency of emitting light of the LED chip itself and the efficiencyof emitting light by the excitation of the fluorescent material, it ismore preferable to set the wavelength of light emitted by the LED chip 5within a range from 450 nm to 475 nm. The present invention can also beapplied to an LED chip that emits light in ultraviolet region of awavelength shorter than 400 nm, by choosing the type of fluorescentmaterial.

Since the nitride semiconductor LED chip based on the insulatingsubstrate such as sapphire or spinel has the p-type and n-typeelectrodes formed on the semiconductor surface side, the electrodes areformed in a desired shape on the p-type semiconductor layer and then-type semiconductor layer by sputtering, vapor deposition or the likeafter etching the p-type semiconductor so as to expose the n-typesemiconductor. When light is extracted from the semiconductor side, theelectrode formed almost all over the surface of the p-type semiconductorlayer is made as a light transmitting electrode consisting of a thinmetal film.

<Fluorescent Substance>

Specific gravity of the fluorescent material is several time that of theliquid resin before curing. Viscosity of a thermosetting resin decreasesconsiderably when heated to cure. As a result, when a liquid resinincluding a fluorescent material is applied to cover an LED chip and isheated to cure, most of the fluorescent material included in the resinis concentrated around the LED chip and sediment.

Since the concentrated particles of the fluorescent material sedimentone on another around the LED chip 5, only the fluorescent materialparticles located near the LED chip surface can efficiently absorb lightemitted by the LED chip. Thus many of the fluorescent material particlesdo not fully perform the wavelength converting function but act only toattenuate the light energy by blocking the light of which wavelength hasbeen converted by the other fluorescent material particles. This resultsin a decrease in the output power of the light emitting diode.

To avoid such a problem, the present invention employs such afluorescent material having a particular particle size distribution asthe wavelength converting function of all fluorescent material particlescan be fully made use of, thereby to improve the output power of thelight emitting diode.

Specifically, the fluorescent material used in the light emitting diodeof the first embodiment consists of a group of fluorescent particles oflarge particle size 81 (first part of distribution) and a group offluorescent particles of small particle size 82 (second part ofdistribution), while there is a region between the first part and thesecond part of the particle size distribution where substantially nofluorescent material exists. According to the present invention, thefluorescent material of such a particle size distribution is used toprevent the formation of precipitation that has adverse effect on theoptical performance and prevent irregular color of the emitted lightfrom occurring. FIG. 2A and FIG. 2B show volume-based distribution curveof the fluorescent material used in the first embodiment, FIG. 2A beingthe cumulative percentage distribution of the particle sizes and FIG. 2Bbeing distribution frequency of the particle sizes.

As shown in FIG. 2A, the fluorescent material used in the presentinvention consists of particles of sizes distributed as shown by thevolume-based distribution curve that has a flat region between thecumulative percentage of 0.01 vol % to 10 vol % where inclination of thecurve is zero. In the flat region, that is a range of particle sizeslocated between the first part and the second part of the distribution,there is substantially no fluorescent material.

In the first embodiment, the fluorescent particles of small particlesize 82 accounts for 0.01 vol % to 10 vol % of the total volume offluorescent material, while the fluorescent particles of large particlesize 81 accounts for 90 vol % or more of the total volume of fluorescentmaterial. According to the present invention, the fluorescent particlesof small particle size preferably accounts for 0.01 vol % to 5 vol % ofthe total volume of fluorescent material. Including the fluorescentparticles of small particle size in such a small amount makes itpossible to disperse the fluorescent material in the resin so as not toblock the light emitted by the LED chip and the fluorescent particles oflarge particle size while preventing irregular color from occurring.

It is also preferable that the peak diameter of the particle sizedistribution of the fluorescent particles of large particle size 81 iswithin a range from 20 to 90 times the peak diameter of the particlesize distribution of the fluorescent particles of small particle size82. When the two groups of particles have such a large difference inparticle size, it is made possible to make full use of the functions ofthe two groups of fluorescent material particles (the fluorescentparticles of small particle size 82 mainly scatter light, and thefluorescent particles of large particle size 81 mainly convert thewavelength).

The fluorescent particles of small particle size 82 has lower efficiencyof wavelength conversion, but can reflect and scatter light therebypreventing irregular color of the emitted light. Therefore, thefluorescent particles of small particle size is preferably dispersed inthe light transmitting resin instead of precipitating around the LEDchip.

The fluorescent particles of small particle size used in the presentinvention are prepared in a very small amount with the particle sizesthereof being far smaller than those of the fluorescent particles oflarge particle size. This allows for the light emitting diode having thefluorescent particles of small particle size favorably dispersed in thelight transmitting resin. Particle sizes of the fluorescent particles ofsmall particle size 82 are preferably within a range from 0.2 to 1.5 μm.This makes it possible to prevent the fluorescent particles of smallparticle size from precipitating and have the function to scatter lightperformed effectively. Also the fluorescent particles of small particlesize 82 of particle sizes described above hardly precipitate in thelight transmitting resin that has not yet cured, and therefore can bedisposed separately from the fluorescent particles of large particlesize 81. Specifically, the fluorescent material of the present inventionconsisting of the fluorescent particles of large particle size 81 andthe fluorescent particles of small particle size 82 exists in such astate in the light transmitting resin that covers the LED chip 5 as thefluorescent particles of large particle size 81 are located near the LEDchip 5 and the fluorescent particles of small particle size 82 aredispersed substantially uniformly in the surrounding thereof. Of thefluorescent material dispersed in this state, the fluorescent particlesof large particle size 81 function to convert the wavelength of thelight emitted by the LED chip 5 and the fluorescent particles of smallparticle size 82 located in the surrounding thereof work to reflect thelight thereby to prevent irregular color of the emitted light.

The fluorescent material of medium particle size may also be includedthat have a peak of particle size distribution at a particle sizebetween those of the fluorescent particles of small particle size 82 andthe fluorescent particles of large particle size 81. It is difficult forthe fluorescent particles of large particle size to absorb and convertall the light to be converted. The fluorescent particles of largeparticle size 81 has a larger surface area and therefore there is someportion of light that is reflected by large fluorescent materialparticles. To counter this difficulty, such fluorescent particles ofmedium particle size are included along with the fluorescent particlesof large particle size 81 that have particle sizes smaller than those ofthe fluorescent particles of large particle size 81 and smaller thanthose of the fluorescent particles of small particle size 82, so thatpart of light that is not absorbed by the fluorescent particles of largeparticle size 81 is absorbed by the fluorescent particles of mediumparticle size and converted to different color. Through efficient colorconversion of the portion of light emitted by the LED chip and reflectedby the surfaces of the fluorescent particles of large particle size asdescribed above, it is made possible to obtain desired chromaticity witha minimum amount of fluorescent material and improve the luminance. Themedian particle size of the fluorescent particles of medium particlesize is preferably within a range from 0.3 to 0.9 times that of thefluorescent particles of large particle size 81, more preferably 0.5 to0.8 times thereof, which makes it possible to efficiently absorb lightreflected on the surface of the fluorescent particles of large particlesize and convert the color thereof.

In general, the efficiency of converting wavelength of light becomeshigher as the particle size of the fluorescent material is larger. Thelight emitting diode of the present invention is made in such aconstitution as all light emitted by the LED chip 5 is efficientlyabsorbed and converted by the fluorescent particles of large particlesize 81, by designing the particle size distribution of the fluorescentparticles of large particle size 81 as described later so that thefluorescent particles of large particle size 81 will not be disposed oneon another around the LED chip 5.

Since the fluorescent particles of large particle size 81 having largerparticle sizes among the fluorescent material particles of the presentinvention are distributed as shown in FIG. 4A and FIG. 4B, the particleshardly precipitate in such a state as the particles are in contact witheach other, but are precipitated while keeping favorable distances fromeach other. As a result, light emitted by the LED chip 5 can be guidednot only to the fluorescent particles of large particle size 81 that arelocated near to the LED chip 5 but also to all the fluorescent particlesof large particle size 81. Consequently, more fluorescent materialparticles can contribute to the conversion of light thereby increasingthe light absorption efficiency and wavelength conversion efficiency ofthe entire fluorescent material.

In order to obtain desired light by using the fluorescent material ofthe prior art of which particle sizes are not properly controlled, it isnecessary to include a large amount of the fluorescent material in theresin. Since this leads to thicker layer of fluorescent material withthe particles piled up one on another, proportion of the fluorescentmaterial particles that do not contribute to the light conversionincreases and the fluorescent material particles that do not contributeto the light conversion block the light. Thus light extraction ratio hasbeen low and high luminance could not be achieved with the fluorescentmaterial of the prior art. When the fluorescent particles of largeparticle size 81 having the mean particle size and the particle sizedistribution properly controlled are used as in the present invention,probability of the fluorescent particles of large particle size 81 toprecipitate densely one on another is low so that the fluorescentparticles of large particle size 81 can be dispersed more sparsely thanin the prior art. Accordingly, because the distance between eachfluorescent material particle and the light emitting surface can be maderelatively shorter, light of which wavelength has been converted can beextracted to the outside while maintaining high luminance without beingabsorbed by the resin.

Basic concept of controlling the particle distribution of thefluorescent particles of large particle size 81 according to the presentinvention has been described above.

According to the present invention, as described above, the lightemitting diode of high luminance and high output power can be achievedby using the fluorescent material consisting of the fluorescentparticles of large particle size 81 and the fluorescent particles ofsmall particle size 82 and making the color conversion layer made fromthe fluorescent particles of large particle size 81 disposed around theLED chip 5 at favorable distances from each other in order to improvethe efficiency of extracting the light to the outside, the lightabsorption ratio and the light conversion efficiency.

In order to fluorescent material particles that do not contribute to thelight conversion efficiency, particle sizes of the fluorescent particlesof large particle size 81 are preferably controlled within a range from10 μm to 60 μm, more preferably from 10 μm to 50 μm and most preferablyfrom 15 μm to 30 μm. Fluorescent particles smaller than 10 μm and largerthan the fluorescent particles of small particle size 82 tend toprecipitate and precipitate densely mass in the liquid resin, therebydecreasing the transmittance of light. Fluorescent particles smallerthan 15 μm and larger than the fluorescent particles of small particlesize 82 have higher tendency to precipitate and precipitate densely inthe liquid resin than those larger than 15 μm and, when the producingprocess is controlled improperly, the particles precipitate densely inthe liquid resin thereby decreasing the transmittance of light.

Particle sizes of the fluorescent particles of large particle size arepreferably uniform which makes it possible to effectively prevent thefluorescent particles of large particle size from precipitating densely.Standard deviation of the particle size distribution of the fluorescentparticles of large particle size can be kept to within the desirablerange of 0.3 or lower without specific classifying operation, and can befurther controlled to 0.15 or lower by classification (the inventors ofthe present application verified that fluorescent particles of largeparticle size having standard deviation of 0.135 can be manufactured byclassification).

The present invention improves the output power of the light emittingdiode by using the fluorescent particles of large particle size asdescribed above thereby minimizing the blocking of the light by thefluorescent material. The material for the fluorescent particles oflarge particle size used in the present invention is preferably one thathas high light absorption ratio, high conversion efficiency and a widerange of excitation wavelengths.

As 90 vol % or more of the fluorescent material consists of thefluorescent particles of large particle size 81 that have excellentoptical characteristics (high light absorption ratio, high conversionefficiency and a wide range of excitation wavelengths), light of otherwavelengths around the main emitting wavelength of the LED chip can besatisfactorily converted to other wavelength and the light emittingdiode can be manufactured more preferably in mass production.

As described above, since the light emitting diode of the presentinvention uses the fluorescent material of the above constitution, thefluorescent material particles can be separated into the layer havingthe function to scatter light made of the fluorescent particles of smallparticle size 82 dispersed in the region apart from the LED chip 5 inthe resin and the color conversion layer made of the fluorescentparticles of large particle size 81 precipitated around the LED chip 5with favorable distances being kept from each other. Thus the lightemitting diode of the present invention capable of emitting light ofhigh output power and high luminance uniformly without irregular colorcan be obtained.

Particle size distribution of the fluorescent material used in thepresent invention is shown by the volume-based distribution curve. Thevolume-based distribution curve is drawn by measuring the particle sizedistribution of the fluorescent material by laser diffraction andscattering method. Specifically, the fluorescent material is dispersedin a aqueous sodium hexametaphosphate solution having a concentration of0.05% and the particle size distribution is measured with a laserdiffraction particle size distribution measuring instrument (SALD-2000A)over a range from 0.03 to 700 μm in an atmosphere of 25° C. intemperature and 70% in humidity.

According to the present invention, median particle size of thefluorescent material refers to the particle size at which the cumulativepercentage reaches 50 vol % in the volume-based distribution curve, andthis value is preferably within a range from 15 to 50 μm. It is alsopreferable that the fluorescent material includes the particles of thismedian size with a high concentration, preferably from 20% to 50 vol%(distribution frequency). The light emitting diode having good contrastwith irregular color suppressed can be obtained by using the fluorescentmaterial made up of particles having less variation in size as describedabove.

This is because, while the fluorescent particles of large particle size81 are more probable to cause irregular color than smaller fluorescentmaterial particles, grading the fluorescent particles of large particlesize 81 to decrease the variations in the particle size improves theirregular color compared to a case of greater variations.

In the light emitting diode of the present invention, the fluorescentmaterial is preferably based on the yttrium aluminum oxide fluorescentmaterial activated with cerium that can emit light by absorbing thelight emitted by the semiconductor LED chip having the light emissionlayer made of a nitride semiconductor.

The yttrium aluminum oxide fluorescent material may be YAlO₃:Ce,Y₃Al₅O₁₂:Ce (YAG:Ce), Y₄Al₂O₉:Ce or a mixture of these materials. Theyttrium aluminum oxide fluorescent material with Ba, Sr, Mg, Ca and/orZn included therein may also be used. Si may also be included tosuppress the reaction of growing crystal so as to obtain the fluorescentmaterial particles of uniform sizes.

In this specification, the yttrium aluminum oxide fluorescent materialactivated with Ce is to be understood in a broad sense of the word so asto include the following fluorescent materials:

(1) yttrium aluminum oxide fluorescent material with part or all yttriumatoms being substituted with at least one element selected from thegroup consisting of Lu, Sc, La, Gd and Sm.

(2) yttrium aluminum oxide fluorescent material with part or allaluminum atoms being substituted with at least one element selected fromthe group consisting of Ba, Tl, Ga and In.

(3) yttrium aluminum oxide fluorescent material with part or all yttriumatoms being substituted with at least one element selected from thegroup consisting of Lu, Sc, La, Gd and Sm and part or all aluminum atomsbeing substituted with at least one element selected from the groupconsisting of Ba, Tl, Ga and In.

More specifically, the fluorescent material is a photoluminescentfluorescent particles represented by general formula(Y_(Z)Gd_(1−Z))₃Al₅O₁₂:Ce (0<Z≦1) or a photoluminescent fluorescentparticles represented by general formula (Re_(1−a)Sm_(a))₃Re′₅O₁₂:Ce(0≦a<1, 0≦b≦1, Re is at least one element selected from among Y, Gs, Laand Sc and Re′ is at least one element selected from among Al, Ga andIn).

The fluorescent material, due to its garnet structure, has highresistance against heat, light and water, and has an excitation spectrumpeaking at around 450 nm and a broad emission spectrum with peakemission at around 580 nm and tailing up to 700 nm.

Efficiency of excitation emission of the photoluminescent fluorescentparticles in a long wavelength region not shorter than 460 nm can beimproved by including Gd (gadolinium) in the crystal. As the Gd contentis increased, peak wavelength of light emission shifts toward a longerwavelength and the entire emission spectrum also shifts toward longerwavelengths. This means that emission of light of more reddish color canbe achieved by increasing the Gd content. Increasing the Gd content alsodecreases the luminance of blue photoluminescence emission. Thefluorescent material may also include Tb, Cu, Ag, Au, Fe, Cr, Nd, Dy,Co, Ni, Ti or Eu added thereto as required.

The emission wavelength also shifts toward shorter wavelengths when apart of Al atoms are substituted with Ga in the yttrium aluminum garnetfluorescent material having a garnet structure. The emission wavelengthalso shifts toward longer wavelengths when a part of Y atoms aresubstituted with Gd.

When substituting a part of Y atoms with Gd, it is preferable to keepthe proportion of Y atoms substituted with Gd within 10% and increasethe Ce content (substitution) from 0.03 to 1.0. When the proportion of Yatoms substituted with Gd is less than 20%, green component increasesand red component decreases but this change can be compensated for byincreasing the Ce content so as to compensate for the decrease in thered component thereby to obtain the desired chromaticity withoutdecreasing the luminance. Because the photoluminescent fluorescentparticles which has such a composition has an excellent temperaturecharacteristic, the reliability of the light emitting diode can beimproved. Also the use of a photoluminescent fluorescent particles thathas been prepared to have much red component makes it possible tomanufacture a light emitting diode capable of emitting an intermediatecolor such as pink.

The photoluminescent fluorescent particles described above can bemanufactured as follows. First, as the materials to make Y, Gd, Al andCe, oxides thereof or compounds that can easily turn into such oxidesare mixed in stoichiometrical proportions thereby to make the stockmaterial. Alternatively, a solution prepared by dissolving rare earthmetals of Y, Gd and Ce in stoichiometrical proportions in an acid iscoprecipitated with oxalic acid, the product of which is fired to obtaina coprecipitated oxide material. The coprecipitated oxide material ismixed with aluminum oxide to obtain a mixed stock material. A mixture ofthe mixed stock material and fluoride such as barium fluoride orammonium fluoride added thereto as a flux is put into a crucible andfired at a temperature from 1350 to 1450° C. in air atmosphere for 2 to5 hours. The fired material is ground in water by using a ball mill,washed, separated, dried and sieved to obtained a photoluminescentfluorescent particles.

In the light emitting diode of the present invention, thephotoluminescent fluorescent particles may contain two or more kinds ofyttrium aluminum garnet fluorescent material activated with ceriumand/or other fluorescent material added thereto.

When two kinds of yttrium aluminum garnet fluorescent material havingdifferent proportions of Y being substituted with Gd are mixed, light ofdesired chromaticity can be obtained easily. Particularly when afluorescent material having higher proportion of substitution is used asthe fluorescent particles of large particle size and a fluorescentmaterial having lower proportion of substitution or no substitution atall is used as the fluorescent particles of medium particle size, colorrendering performance and luminance can be improved at the same time.

<Light Transmitting Resin>

The light transmitting resin 8 is formed by applying a solution, whichis prepared by mixing a crosslinked oligomer obtained by reacting anepoxy resin containing an alicyclic epoxy resin, which accounts for 65%by weight or more of the epoxy resin, with an acid anhydride ordicarboxylic acid (0.005 to 1.5 mol based on an epoxy equivalent) with asmall amount of a cation curing agent (0.00005 to 0.003 mol, preferably0.0001 to 0.01 mol, based on an epoxy equivalent), to the inside of amounting area 1 a in which the LED chip 5 of the nitride semiconductoris mounted, followed by curing with heating.

The light transmitting resin 8 thus formed scarcely causes yellowing ofthe resin because the content of the cation curing agent that absorbsblue light is 1/10 to 1/100 times as much as that in the prior art.Therefore, the light emitted by the LED chip of the nitridesemiconductor capable of emitting blue light and light of whichwavelength has been converted can be extracted to the outside. Becauseof comparatively high pliability, the light transmitting resin 8 reducesthe thermal stress caused by a difference in thermal expansioncoefficient between the light transmitting resin 8 and the LED chip 5,thus making it possible to prevent failures such as crack in the LEDchip 5 of the nitride semiconductor and breakage of the wire 7.

The composition of the epoxy resin composition used in the lighttransmitting resin 8 will now be described in detail.

The epoxy resin composition constituting the light transmitting resin 8contains, as an essential component, an epoxy resin containing analicyclic epoxy resin as a main component, an acid anhydride ordicarboxylic acid, and a cation curing agent. If necessary, it furthercontains a promotor made of a polyhydric alcohol or a polycondensatethereof. Details of the respective components are as follows.

(Epoxy Resin)

Since the light transmitting resin 8 must maintain high lighttransmittance, it is required that the epoxy resin used in the presentinvention accounts for 65% by weight or more, preferably 90% by weightor more, of the whole epoxy resin component (total amount of only theepoxy resin excluding a curing agent) and the content of an aromaticcomponent serving as a coloring component, especially a phenolderivative, is reduced as small as possible. As the alicyclic epoxyresin, for example, epoxidated cyclohexene derivative, hydratedbisphenol A diglycidyl ether and diglycidyl hexahydrophthalate ester canbe used alone or in combination. It is particularly preferred to mix anepoxidated cyclohexene derivative such as3,4-epoxycyclohexylmethyl-3′,4′-epoxyhexyl carboxylate, as a maincomponent, with diglycidyl hexahydrophthalate ester and, if necessary,an epoxy resin made of a cyclohexane derivative such as hydrogenatedbisphenol A diglycidyl ether, and epichlorohydrin. A liquid or solidepoxy resin made of bisphenol A diglycidyl ether can also be mixed, ifnecessary.

(Acid Anhydride or Dicarboxylic Acid)

As the acid anhydride or dicarboxylic acid, an acid anhydriderepresented by the following general formula (1) or dicarboxylic acidrepresented by the following general formula (2).

In the formulas, R₁ represents a cyclic or aliphatic alkyl or arylhaving 0 to 12 carbon atoms and R₂ represents an alkyl or aryl having 0to 12 carbon atoms. As the acid anhydride, for example, there can beused propionic anhydride, succinic anhydride,1,2-cyclohexanedicarboxylic anhydride,3-methyl-1,2-cyclohexanedicarboxylic anhydride,4-methyl-1,2-cyclohexanedicarboxylic anhydride, phthalic anhydride,4,4′-biphthalic anhydride, hexahydrophthalic anhydride,methylhexahydrophthalic anhydride, trialkyltetrahydrophthalic anhydride,and hydrated methyl nadic anhydride. As the dicarboxylic acid, forexample, there can be used 4,4′-biphenyldicarboxylic acid,2,2′-biphenyldicarboxylic acid, oxalic acid, succinic acid, adipic acid,1,6-hexanedicarboxylic acid, 1,2-cyclohexanedicarboxylic acid,1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid,o-phthalic acid, m-phthalic acid, and p-phthalic acid.

When an epoxy resin is mixed with an acid anhydride or dicarboxylic acidto form a crosslinked oligomer and then the crosslinked oligomer iscured by mixing a cation curing agent, the acid anhydride ordicarboxylic acid is mixed in the amount within a range from 0.005 to0.5 mol, and preferably from 0.01 to 0.2 mol, based on an epoxyequivalent. When the epoxy resin, the acid anhydride or dicarboxylicacid and the cation curing agent are simultaneously mixed and cured, theacid anhydride or dicarboxylic acid is mixed in the amount within arange from 0.005 to 1.5 mol, and preferably from 0.1 to 0.8 mol, basedon an epoxy equivalent.

(Cation Curing Agent)

As the cation curing agent, for example, there can be used aromaticsulfonium salt, aromatic diazonium, aromatic iodonium salt and aromaticselenium. The aromatic sulfonium salt is decomposed by heat and/orultraviolet light having a wavelength of 360 nm or less to generate acation. Examples thereof include Triphenyl sulfoniumHexafluoroantimonate and Triphenyl sulfonium Hexafluorophosphate. Theresin composition can be sufficiently cured by adding a small amount ofTriphenyl sulfonium Hexafluoroantimonate because of its large curingrate. The cation curing agent is preferably used in the amount within arange from 0.00005 to 0.003 mol, preferably from 0.0001 to 0.01 mol, andmore preferably from 0.0002 to 0.005 mol, based on an epoxy equivalent.

(Promotor)

Examples of the polyhydric alcohol used as a promotor include ethyleneglycol, diethylene glycol, trimethylene glycol, triethylene glycol,propylene glycol, 1,4-butanediol, and 1,6-hexanediol. There can also beused a polycondensate obtained by the condensation polymerization of oneor more polyhydric alcohols among these polyhydric alcohols. Thepolyhydric alcohol or polycondensate thereof is used in the amountwithin a range from 0.1 to 5.0 equivalents, and preferably from 0.2 to3.0 equivalents, based on the acid anhydride or dicarboxylic acid.

The epoxy resin composition used in the light transmitting resin 8 maycontain component other than those described above. For example, thelight transmitting resin 8 may contain fillers 10. In addition to thefillers 10, it can contain various functional particles of diffusingagents and colorants.

The method of forming the light transmitting resin 8 will now bedescribed in detail.

The method of forming a light transmitting resin 8 includes, forexample, (i) a method of applying a solution, which is prepared bysimultaneously mixing an epoxy resin with an acid anhydride and a cationcuring agent, and curing the solution, and (ii) a method of applying asolution, which is prepared by reacting an epoxy resin with an acidanhydride to form a crosslinked oligomer and mixing the crosslinkedoligomer with a cation curing agent, and curing the coating film. Forexample, when the light transmitting resin 8 is formed in the thicknessof 500 μm or less, the method (ii) is better. By employing the method(ii), volatilization of the acid anhydride can be prevented in case ofapplying the light transmitting resin 8 in the form of a thin film andcuring the thin film. Also the viscosity of the solution to be appliedis easily controlled and the pot life is prolonged, so that theworkability is improved.

The method (ii) will now be described.

First, an epoxy resin containing an alicyclic epoxy resin, whichaccounts for 65% by weight or more of the epoxy resin, is reacted withan acid anhydride or dicarboxylic acid in the amount within a range from0.005 to 0.5 mol, preferably from 0.01 to 0.20 mol, based on an epoxyequivalent to form a crosslinked oligomer in a proper reaction vessel.When using a polyhydric alcohol or a polycondensate thereof as apromotor, it is mixed with the epoxy resin, together with an acidanhydride or dicarboxylic acid. The reaction between the epoxy resin andthe acid anhydride or dicarboxylic acid is preferably conducted at roomtemperature at which the side reaction such as oxidation is less likelyto occur. In the case of the acid anhydride, the reaction time is withina range from about 1 to 360 hours. In the case of the dicarboxylic acid,the reaction time is within a range from about 1 to 180 hours. To reducethe reaction time by acceleration of the ring-opening reaction of theacid anhydride, the reaction system may be heated to 50 to 150° C.(preferably 60 to 120° C.).

Then, a solution is prepared by mixing the resulting crosslinkedoligomer with a cation curing agent in the amount within a range from0.00005 to 0.03 mol, preferably 0.0001 to 0.01 mol, based on an epoxyequivalent. The mixed solution is packaged in the inside of a mountingarea 1 a in which the LED chip 5 of the nitride semiconductor ismounted, and then cured with heating to form a light transmitting resin8. Preferably, the mixed solution is subjected to primary curing byheating at 80 to 100° C. for 2 to 4 hours and then subjected tosecondary curing by heating at 140 to 150° C. for 2 to 4 hours.

More specific method will be described hereinafter.

The pliability of the epoxy resin composition thus obtained finally isproportion to the molecular weight of the crosslinked oligomer duringthe process. The higher the proportion of carboxyl groups, which areconverted into an ester as a result of the reaction with the epoxy resinor promotor, among carboxyl groups of the acid anhydride or dicarboxylicacid, the better the pliability of the resulting epoxy resincomposition. The viscosity of the mixed solution of the crosslinkedoligomer and the cation curing agent can be freely controlled byadjusting the amount of the acid anhydride or the ester conversionratio, because the viscosity varies depending on the molecular weight ofthe crosslinked oligomer.

<Manufacturing Method of Embodiment 1>

Now a method for producing the light emitting diode of the firstembodiment will be described below.

This producing method is a method for producing the surface mountedlight emitting diode of the first embodiment with stable qualitysatisfactorily in mass production.

In this producing method, since a plurality of packages are processedcollectively to the step of covering the LED chip 5 with the lighttransmitting resin, a package assembly consisting of a plurality ofpackages is used. The package assembly is made by bonding an insulatingsubstrate 101 having a plurality of through holes 101 a that correspondto a mounting area 1 a of each package, and a metal base plate 102.

The insulating substrate 101 comprises, for example, a laminated resinof thickness from 0.06 mm to 2.0 mm and has a plurality of through holes101 a penetrating therethrough in the direction of thickness. Crosssection of the through hole 101 a may be oval, circular or rectangular.That is, the present invention is not limited in terms of the crosssectional shape of the through hole 101 a that can be selected fromamong various shapes. Inner wall of the through hole 101 a is preferablytapered neat the opening so that the diameter thereof increases from oneside of the insulating substrate (surface to be bonded with a thin metalsheet) toward the other side. When the inner wall of the through hole101 a is tapered, light emitted by the LED chip toward the inner wallcan be reflected thereon and directed upward, thus making it possible toextracting the light emitted by the LED chip 5 efficiently from thelight emitting element.

The metal base plate 102 has separation grooves formed therein incorrespondence to the through holes with the grooves filled with aninsulating resin 4, so that thin metal sheet 2 a and the thin metalsheet 2 b are electrically isolated from each other by the insulatingresin 4 in each package when the packages are cut off.

A part of thin metal sheet 2 a, the insulating resin 4 and a part of thethin metal sheet 2 b are exposed in the through hole 101 a in eachpackage.

Also in the package assembly, the plurality of packages are disposed ina group for each opening 113 of the mask 112 to be described later.

<Mounting of LED Chip>

The LED chips 5 are die-bonded at predetermined positions in the throughholes (mounting areas) of the package assembly constituted as describedabove, and wiring is provided as required by wire bonding (FIG. 5).

The thin metal sheet 2 a and the thin metal sheet 2 b are exposed in thethrough hole, and the LED chip 5 is bonded onto the thin metal sheet 2 bthat is a negative electrode, while a p-type electrode 5 a and an n-typeelectrode 5 b of the LED chip 5 are connected to the thin metal sheet 2a and the thin metal sheet 2 b, respectively by means of wires 7.

<First Process: Mimeograph Printing>

The light transmitting resin (epoxy resin composition of the presentinvention) 8 that serves as the sealing member is applied by mimeographprinting in a chamber. FIG. 3A is a plan view of the mask 112 used inthe mimeograph printing according to the producing method of the firstembodiment. The mask 112 has a plurality of apertures 113 as shown inFIG. 3A, position and size of each aperture 113 being set so that aplurality of packages of one group correspond to one of the apertures113 (FIG. 3B). Thus the mask used in the present invention is designedso as to form the light transmitting resin layer not only in the throughholes but also in the surrounding thereof on the insulating substrate101. According to the producing method of this embodiment, such a lighttransmitting resin layer that maintains a smooth surface even aftercuring can be formed on the inner surfaces of the through holes 101 a ofthe insulating substrate and on the insulating substrate 101 by carryingout the mimeograph printing using the mask 112 as described above.

Specifically, in this producing method, groups each consisting of aplurality of packages are disposed except for areas around the apertures113 where it is difficult to apply the light transmitting resin with aflat surface, as shown in FIG. 5. Thus the light transmitting resinlayer having uniform thickness and flat surface is formed in theportions where the plurality of packages are disposed, so as to suppressthe variations in the thickness of the light transmitting resin layerbetween packages and make the light transmitting resin surface of eachpackage flat.

After forming the light transmitting resin layer in a single step forthe plurality of light emitting diodes as described above, individuallight emitting diodes are separated by cutting along the dashed linesshown in FIG. 5. Thus the light emitting diodes having uniform thicknesscan be manufactured with high yield without variations in the size andcolor among the light emitting diodes. Thickness of the lighttransmitting resin layer formed on the insulating substrate can bechanged freely by controlling the thickness of the mask.

Now an example of method for the light transmitting resin layer havinguniform thickness and flat surface in the portions where the pluralityof packages are disposed around the apertures 113 will be describedbelow.

(Step 1)

First, the package assembly 100 having the through holes 101 a facingtoward the mask 112 is sucked onto a elevation stage 117 (FIG. 4A), thestage 117 is lifted with the package assembly 100 and the mask 112aligned and put into contact with the bottom surface of the mask 112(FIG. 4B). This makes it possible to bring the package assembly 100 intocontact with the mask 112 in such a state as warping of the packageassembly being corrected. As warping of the package assembly iscorrected as described above, the light transmitting resin layer ofuniform thickness can be formed on one surface of the package assembly100. Forming the sealing member in the warped state on the substrateleads to variations in thickness among the light emitting diodes, thusresulting in lower yield.

The light transmitting resin that includes the fluorescent material isapplied on outside of the apertures of the mask 112 under theatmospheric pressure as shown in FIG. 4A, and the resin is deaerated bydecreasing the pressure in this condition. The decreased pressure ispreferably within a range from 100 to 400 Pa, which makes it possible toeffectively remove bubbles from the resin. In this embodiment in whichthe package assembly 100 and the mask 112 are used, the lighttransmitting resin having a relatively high viscosity can be used.

In case the fluorescent material is used while being included in thelight transmitting resin as in the first embodiment, it is preferable touse a resin that has a certain level of viscosity in order to ensurehomogeneous dispersion, since the fluorescent particles of largeparticle size precipitate at a fast rate in the liquid resin. However, aresin of higher viscosity is difficult to deaerate and may lead to loweryield of production. For this reason, in the present invention, themimeograph printing is carried out while repeating the pressurizationand depressurization after removing bubbles by decreasing the pressure,so as to make it possible to use the light transmitting resin of highviscosity without decreasing the yield of production. Thus a resin ofhigh viscosity can be used in order to minimize the color inconsistencythat tends to occur when fluorescent particles of large particle sizeare used. Also the light emitting diode can be manufactured with highyield even when a resin of high viscosity is used.

In case sealing is done with the light transmitting resin includingbubbles, the bubbles reflect and refract light emitted by the LED chipand light emitted by the fluorescent material, resulting in conspicuousirregular color and unevenness in luminance. To prevent this problem, itis very effective in suppressing irregular color and unevenness inluminance, to repeat the cycle of decreasing and increasing the pressureas in this embodiment when applying the light transmitting resin thatincludes the fluorescent material. Bubbles included in the lighttransmitting resin may also lead to peel-off of the light transmittingresin and/or wire-bonded portion and wire breakage, resulting in lowerreliability. Therefore removal of the bubbles by the method of thisembodiment is very effective also in improving the reliability.

<Step 2>

Then first cycle of forward squeegee sweep is carried out underdecreased pressure (FIG. 4C). A forward squeegee spatula 114 used inthis operation is inclined forward with respect to the vertical line ofthe mask 112 as shown in FIG. 4C, and is pressed by pneumatic pressureagainst the mask 112 so as to move and squeeze the resin 8 into theaperture 113 of the mask 112. Since the forward squeegee sweepingoperation is carried out under decreased pressure, suction of theelevation stage 117 is not effective. But displacement between thepackage assembly 100 and the mask 112 does not occur because theelevation stage 117 is pressed physically against the mask 112.

<Step 3>

Then the ambient pressure is increased to the atmospheric pressure and,upon completion of pressure increase, first cycle of return squeegeesweep is carried out in a direction opposite to the forward squeegeesweep (FIG. 4D). A return squeegee spatula 115 is inclined toward themoving direction with respect to the vertical line of the mask 112 moresteeply than the forward squeegee spatula 114 and is moved by largerpneumatic pressure than that in the forward squeegee sweep operation. Asthe light transmitting resin is squeezed again with a larger contactarea between the return squeegee spatula 115 and the mask 112, bubblescan be removed efficiently from the resin that fills the apertures 113so that the sealing member can be finished with smoother surface.

<Step 4>

Several cycles of forward and return squeegee sweeping operations arecarried out while repeating the pressure decreasing and increasingcycles similarly to the step 2 and step 3, thereby to fill the aperture113 with the resin of uniform thickness.

<Step 5>

With the mask 112 in contact with the package assembly 100, the lighttransmitting resin is cured and then the mask is removed. Thus the lighttransmitting resin formed integrally in the through hole wherein the LEDchip is placed and on the top surface of the insulating substrate can bemade to have top surface that is flat and substantially parallel to thebottom surface of the package.

When the method of forming the sealing resin by mimeograph printing isemployed as described above, the light transmitting resin havingrelatively high viscosity before curing can be used. Consequently,unlike in the case of using a resin of low viscosity, the fluorescentmaterial does not precipitate or migrate in the resin. As a result,relatively good mixed state of the fluorescent material can bemaintained. In addition, the period in which the light transmittingresin remains during the forming process is from several tens of secondsto several minutes, far shorter than several hours in the case ofpotting process in which molten resin is poured into the through holesand cured by heat. Moreover, since the time taken to cure can also bemade very short, the fluorescent material particles can be preventedfrom precipitating one on another on the LED chip.

Thus according to the producing method of the first embodiment, sincethe light transmitting resin of high viscosity can be used, the resinand the fluorescent material can be prevented from separating from eachother in the period after mixing the fluorescent material in the lighttransmitting resin till application to the substrate. As a result,variations in the content of fluorescent material included in the resinamong the light emitting diodes can be minimized, thus making itpossible to manufacture the light emitting diodes with less variation inthe color of the emitted light within a production lot and amongdifferent production lots. Yield of production can also be improved.

Also the fluorescent particles of large particle size can be preventedfrom precipitating densely near the surface of the LED chip in theperiod between filling the through holes and curing of the resin, sothat wavelength converting function of the fluorescent particles oflarge particle size can be effectively utilized. Further, thefluorescent particles of small particle size can be distributeduniformly in the light transmitting resin around the fluorescentparticles of large particle size, thus preventing light emitting diodesfrom experiencing irregular color.

Particularly in case the light emitting diode includes YAG:Cefluorescent material as the fluorescent material so as to emit whitelight, the fluorescent material has larger specific gravity than thelight transmitting resin and tends to precipitate densely. Even in thiscase, the fluorescent particles of large particle size 81 can beprevented from precipitating densely near the surface of the LED chip 5,so that the light emitting diodes of uniform color temperature can bemanufactured reliably.

Now the dicing process will be described in detail below. Individuallight emitting diodes are separated through the dicing process asdescribed below after the light transmitting resin has been cured.

<Second Process: Dicing Process>

(Dicing Step 1)

After curing the resin, the package assembly 100 is bonded onto a dicingsheet on the light transmitting resin side. The bonding strength can beincreased since the bonding surfaces of the package assembly 100 and thedicing sheet are made of substantially the same material and are flatplanes. As a result, the chips can be prevented from coming off andmis-positioning in dicing can be prevented, making possible to separateinto the individual light emitting diodes with high yield.

In case the resin is applied and cured by using a mask that hasapertures corresponding to the individual through holes of the packageassembly, in contrast, the applied resin shrinks and sinks over thethrough holes, resulting in decreased bonding strength because only thesurface of the insulating substrate other than the areas over thethrough holes makes contact with the dicing sheet. In case a largeramount of the resin is applied and cured by using the mask that hasapertures corresponding to the individual through holes, on the otherhand, the resin surface becomes higher than the top surface of theinsulating substrate that is to be diced and only the resin surfacemakes contact with the dicing sheet as the bonding surface, thusresulting in very weak bonding strength between the package assembly andthe dicing sheet that leads to mis-positioning in dicing. When dicing iscarried out with the package assembly and the dicing sheet held togetherin unstable condition as described above, the chips tend to come off andmis-positioning in dicing is likely to occur. The light emitting diodesthus obtained may also have such undesirable cut surfaces that haveburrs or the like. The burrs may break in the packaging process thatfollows. When the burrs break to a depth, moisture infiltrates from theoutside into the sealing member. This decreases the reliability of thelight emitting diode and causes such defects as metallic members sealedinside are oxidized and discolor.

<Step 2>

The package assembly that is fixed closely on the dicing sheet in step 1is cut off by means of a dicing blade applied onto the bottom surface ofthe package assembly along the dashed lines in FIG. 5. The dicing bladehas a cutting edge consisting of fine diamond particles around a bond.The diamond blade of this constitution tends to be loaded with metalchips generated as saw dust when cutting off the light emitting diodesthat fill the space between the diamond particles. In order to avoidthis problem, it is preferable to include a hard filler in the lighttransmitting resin that makes the sealing member in the first process,in which case the loading metal chips are pushed out so that dicingoperation can be carried out smoothly. Use of a filler of largerparticle size increases the operation and effect. Using the fluorescentparticles of large particle size as a filler increase the effect sincethe fluorescent particles of large particle size has high hardness.

In the light emitting diode manufactured by the producing methoddescribed above, the light transmitting resin seal is formed integrallyon the top surface of the insulating substrate and in the through holeof the insulating substrate, top surface of the light transmitting resinis substantially parallel to the bottom surface of the package, and theouter circumferential surface of the light transmitting resin issubstantially flush with the outer circumferential surface of thepackage. As the light transmitting resin is formed over the entiresurface of the light emitting diode, light emitting surface can be madewider with increased output power. Moreover, since the lighttransmitting resin on the insulating substrate diffuses light from theLED chip more effectively to the outside, the light emitting diode hasgood directivity. In case the light transmitting resin includes thefiller, the effect is further enhanced by the filler, so that the lightemitting diode has favorable light emitting characteristics.

In the light emitting diode of the first embodiment according to presentinvention, the luminous intensity and power can be increased by usingflorescent material classified so as to have the fluorescent particlesof small particle size and the fluorescent particles of large particlesize and disposing the florescent material to make full use of eachfunction. The fluorescent particles of small particle size account for0.01 vol % to 10 vol % of the total volume of fluorescent material andare dispersed in the transmitting resin to scatter the light. Thefluorescent particles of large particle size can convert the wavelengthof the light efficiently by controlling the particle size thereof sothat the particles can be distributed in the vicinity of the LED chip.Since the fluorescent particles of large particle size of thisembodiment can be excited by the light in a broad wavelength band, thefluorescent particles can convert the wavelength of the light in thecase that the wavelength of the light emitted from the LED chip variesby a change of the current. Therefore, it is possible to provide thelight emitting diode with a good reliability and a good productivity.

In the method for producing the light emitting diode according to thisembodiment, the light emitting diode with a good luminancecharacteristic can be produced efficiently. Moreover, in the case thatproduction process need a long period time, variations in the lightemission performance can be kept extremely small between the lightemitting diodes manufactured in the early stage of the production runand the light emitting diodes manufactured in the latter stage of theproduction run. Therefore, the irregular color of the light emittingdiode can be prevented and the yield of production-can be improved.

The epoxy resin composition of the present invention described in thefirst embodiment can be prevent yellowing and has a high pliability,because a crosslinked oligomer formed by reacting the alicyclic epoxyresin reacts with the acid anhydride or dicarboxylic acid.

The epoxy resin composition of present invention can be handled easily,since the viscosity of the epoxy resin composition can be freelycontrolled by the amount of the acid anhydride or the dicarboxylic acid,or the ester conversion ration and has long pot life.

Embodiment 2

FIG. 6 is a schematic sectional view of an SMD type light emitting diodeaccording to second embodiment of the present invention. The lightemitting diode of the second embodiment comprises the LED chip 5 made byforming a pn junction of a nitride semiconductor (Al_(X)Ga_(Y)In_(Z)N,0≦X≦1, 0 Y≦1, 0≦Z≦1, X+Y+Z=1) on a sapphire substrate via a buffer layermade of Ga_(d)Al_(1−d)N, 0≦d≦1), the LED chip 5 being placed on a glassepoxy substrate 12 that has a pair of lead electrodes 12 a, 12 b. TheLED chip 5 has a light emitting layer made of at least a nitridesemiconductor layer. Positive and negative electrodes provided on atleast one surface of the LED chip 5 are electrically connected to leadelectrodes 12 a, 12 b with electrically conductive wires 7.

In the light emitting diode of the second embodiment, a fluorescentmaterial similar to that of the first embodiment is dispersed in thelight transmitting resin 18.

The fluorescent material dispersed in the light transmitting resin 18consists of the fluorescent particles of large particle size 81 and thefluorescent particles of small particle size 82. Thus the wavelengthconverting function of all the fluorescent particles of large particlesize 81 is fully made use of thereby to improve the output power of thelight emitting diode, while preventing irregular color from occurring bymeans of the fluorescent particles of small particle size 82.

In the light emitting diode of this present invention, epoxy resindescribed in the first embodiment is preferably used for the lighttransmitting resin 18.

However, in the second embodiment, since the resin is molded on thesubstrate instead of filling the inside of the package, other epoxyresin, glass, silicone resin, acrylic resin or the like suitable for theproducing method may also be used.

Embodiment 3

The light emitting diode according to the third embodiment of thepresent invention comprises an LED chip having a constitution, forexample, shown in FIG. 1 or FIG. 6 capable of emitting ultraviolet raywith a main peak of emission in a short wavelength region around 400 nm.An LED chip capable of emitting ultraviolet ray can be easily made bygrowing a semiconductor layer based on a nitride semiconductor on asapphire substrate.

In the light emitting diode of the third embodiment, a resin or glassthat is somewhat resistant to the ultraviolet ray is used as the lighttransmitting resin, and a fluorescent material having the particle sizedistribution described in the first embodiment is used.

For the material of the fluorescent material, Y₂O₂S:Eu fluorescentmaterial that is excited by light of short wavelengths in theultraviolet region and emits red light, Sr₅ (PO₄)₃Cl:Eu fluorescentmaterial that is excited by light of short wavelengths in theultraviolet region and emits blue light or (SrEu)O.Al₂O₃ that is excitedby light of short wavelengths in the ultraviolet region and emits greenlight can be used.

A light emitting diode that emits white light can be manufactured byforming a wavelength conversion layer made of a mixture of a red lightemitting fluorescent material, a blue light emitting fluorescentmaterial and a green light emitting fluorescent material on the surfaceof the LED element.

Besides the fluorescent material described above, 3.5 MgO.0.5MgF₂.GeO₂:Mn, Mg₆As₂O₁₁:Mn, Gd₂O₂:Eu or La₂O₂S:Eu may be used as the redfluorescent material, Re₅(PO₄)₃Cl:Eu (Re is at least one elementselected from among Sr, Ca, Ba and Mg), BaMg₂Al₁₆O₂₇:Eu, or the like maybe used as the blue fluorescent material. The light emitting diodecapable of emitting white light with high luminance can be made by usingthese fluorescent materials.

In the light emitting diode of the third embodiment, since thefluorescent material consists of the fluorescent particles of largeparticle size 81 and the fluorescent particles of small particle size 82similarly to the first embodiment, the wavelength conversion layercapable of efficiently converting light of ultraviolet region is formedso that the light emitting diode of high luminance can be obtained.Particularly when fluorescent materials of a plurality of types are usedto emit mixed light, it is preferable since irregular color can beeffectively suppressed by the light scattering effect of the fluorescentparticles of small particle size.

When a thin layer having wavelength converting function is formed from amixture of such fluorescent materials described above, the fluorescentmaterials preferably have similar median particle size and particleshape, since this makes it possible to satisfactorily mix light ofdifferent wavelengths emitted by the different fluorescent materialsthereby to suppress irregular color.

In the third embodiment, different wavelength conversion layers may alsobe formed from different fluorescent materials. In case differentwavelength conversion layers of different fluorescent materials areformed in multiple layers, it is preferable to form a red light emittingfluorescent material, a green light emitting fluorescent material and ablue light emitting fluorescent material one on another in this order onthe LED chip in consideration of the transmittance of each fluorescentmaterial for ultraviolet ray, since this causes all layers toefficiently absorb light in the ultraviolet region. Furthermore, it ispreferable that the particle sizes of different fluorescent materialsare controlled so that the blue fluorescent material has the largestmedian particle size followed by the green fluorescent material and thenthe red fluorescent material in order to have the particle sizes of thefluorescent material decrease from the lower layer to the upper layer inthe multiple wavelength conversion layers, since this allows ultravioletrays to efficiently transmit up to the topmost layer and also makes itpossible to have the ultraviolet rays completely absorbed by themultiple wavelength conversion layers.

The wavelength conversion layers for different colors may also be formedon the LED chip in such a configuration as stripes, grating or triangle.In this case, the layers including the different fluorescent materialsmay be disposed at a distance from each other, which improves the colormixing performance. It is also preferable to form the wavelengthconversion layer so as to cover the LED chip as a whole, since thismakes it possible to prevent the ultraviolet rays from being absorbed inthe outside of the sealing resin.

Embodiment 4

Fourth embodiment of the present invention relates to a method forproducing the fluorescent material that is suited for the light emittingdiode, in which such a fluorescent material is synthesized thatchromaticity of the emitted light can be prevented from shifting and redcomponent can be prevented from decreasing.

A method for synthesizing the fluorescent material is disclosed inJapanese Unexamined Patent Publication No. 4985/1973 in which variousmaterials of fluorescent material are mixed in stoichiometricalproportions and boric acid is added thereto as flux, with the mixturebeing fired. Japanese Unexamined Patent Publication No. 36038/1986discloses such a method as various materials of fluorescent material aremixed in stoichiometrical proportions and barium fluoride is addedthereto as flux, with the mixture being processed to grow particles.

When barium fluoride and boric acid is added as the flux to thefluorescent material so as to assist the growth of particles,chromaticity of the emitted light obtained by the irradiation withexcitation light shifts and the red component decreases.

In the fourth embodiment, shift in chromaticity of the emitted light offluorescent material is suppressed by adding a liquid to the mixturebefore firing the mixture of the mixed materials of fluorescentmaterials and the flux including barium fluoride. It is supposed thataddition of the liquid during firing makes the mixed materials denserand improves reactivity so that homogeneous fluorescent particles ofuniform particle sizes can be obtained. The effect can be improvedfurther by pressurizing during firing.

The more the amount of the liquid added, the better the particle shapeand the higher the effect of suppressing the chromaticity shift of theemitted light. The amount of the liquid added is preferably within arange from 5 to 200 wt %, more preferably within a range from 10 to 70wt % and most preferably within a range from 50 to 70 wt % of the mixedmaterial. The above effect can be enhanced by adding Fe in addition toCe as the activation agent for the fluorescent material.

Also according to the method for producing, it is preferable to fire thefluorescent material of the fourth embodiment, the mixture of the mixedmaterials of fluorescent materials and the flux in two steps comprisinga first firing step of firing in an air or weakly reducing atmosphereand a second firing step of firing in a reducing atmosphere.

In the present invention, the weakly reducing atmosphere refers to anatmosphere that includes oxygen of such a concentration that at leastthe quantity of oxygen required in the reaction of forming the desiredfluorescent material from the mixed material. The fluorescent materialcan be prevented from blackening and the light absorbing efficiency canbe prevented from decreasing, by carrying out the first firing stepuntil the process of forming the desired fluorescent material iscompleted in the weakly reducing atmosphere. The reducing atmosphere inthe second firing step is a reducing atmosphere that has higher reducingpower than the weakly reducing atmosphere.

A fluorescent material having high efficiency of absorbing excitationlight can be obtained by firing in two steps as described above. Thismakes it possible to reduce the amount of the fluorescent materialrequired to obtain the desired chromaticity and obtain a light emittingdiode having high efficiency of extracting light, for example, when themethod is applied to the light emitting diode.

Variation Example 1

(Light Transmitting Resin)

While a particular epoxy resin is used in the first embodiment,according to the present invention, the light emitting diode may also bemade by mixing other resin or glass and the fluorescent materialdescribed in the first embodiment.

In this case, materials that can be suitably used as the lighttransmitting resin include light transmitting resins having goodweatherability such as other type of epoxy resin (for example,nitrogen-containing epoxy resin), acrylic resin and silicone and glass.A light emitting diode of high output power can be made also byincluding fluorescent material consisting of fluorescent particles oflarge particle size and fluorescent particles of small particle size insuch a resin as described above. A pigment may also be added togetherwith the fluorescent material to the light transmitting resin.

In order to improve weatherability of the light transmitting resin, anultraviolet absorbing agent may also be added to the light transmittingresin, and further an antioxidant, organic zinc carboxylate, acidanhydride or chelate compound of zinc may also be added to the lighttransmitting resin.

Variation Example 2

(Diffusing Agent)

Further according to the present invention, the light transmitting resinmay include a diffusing agent in addition to the fluorescent material.For the diffusing agent, barium titanate, titanium oxide, aluminumoxide, silicon oxide, calcium carbonate or the like is preferably used.Organic diffusing agents such as melanin resin, CTU guanamine resin andbenzoguanamine resin can also be used.

The light emitting diode having good directivity can be made by addingthe diffusing agent as described above.

The diffusing agent in this specification has median particle size of 1nm or over and less than 5 μm. It is preferable to use the diffusingagent having median particle size within a range from 1 μm to 5 μm,since it causes satisfactory random reflection of light emitted by theLED chip and the fluorescent material and suppression of irregular colorthat tends to occur when the fluorescent particles of large particlesize is used. Use of the diffusing agent also makes it possible to makethe half width of the light emission spectrum narrower and obtain thelight emitting diode having high color purity.

The diffusing agent having median particle size or 1 nm or over and lessthan 1 μm has lower effect of interfering with the light emitted fromthe LED chip but can improve the viscosity of the resin withoutdecreasing the luminous intensity. When this effect is utilized in aprocess of filling the recess of package with a resin by potting or thelike, it is made possible to disperse the fluorescent materialsubstantially uniformly in the resin that is contained in a syringe andmaintain this condition, and therefore high yield of production can beachieved even when the fluorescent particles of large particle size thatis relatively difficult to handle is used. As can be seen from the abovediscussion, the diffusing agents used in the present invention havedifferent actions depending on the range of particle sizes, and can beused in proper combinations according to the application.

Variation Example 3

(Filler)

Further according to the present invention, the light transmitting resinmay contain fillers, in addition to the fluorescent material. Specificmaterial that can be used as the filler are the same as those for thediffusing agent, although the median particle size is different. Thefiller in this specification has median particle size within a rangefrom 5 μm to 100 μm. When the filler having median particle size in thisrange is included in the light transmitting resin, variation in thechromaticity of light emitted by the light emitting diode is improved bythe light scattering effect and resistance of the light transmittingresin against the thermal shock can be improved. This makes it possibleto prevent such troubles as breakage of wires that connect the LED chipand electrodes of the package and peel off of the bottom surface of theLED chip and the bottom of the package recess even when used at hightemperatures. Thus the light emitting diode of high reliability can beprovided. Moreover, it is made possible to regulate the fluidity of theresin at a constant level over an extended period of time and applying arequired amount of the light transmitting resin to a desired position,thus allowing for mass production with a high yield.

The filler has preferably similar particle size and/or shape to those ofthe fluorescent material. In this specification, the expression “similarparticle size” means that the difference in the median particle size isless than 20%, and the expression “similar shape” means that thedifference in the roundness factor (length of circumference of a truecircle of the same area as the projected area of the particle/lengthprojected of circumference of the particle) that represents the degreeof proximity of the particle shape to the true circle is less than 20%.Use of such a filler results in interaction of the fluorescent materialand the filler that causes the fluorescent material to be favorablydispersed in the resin thereby to suppress the irregular color. Both thefluorescent material and the filler preferably have median particlesizes within a range from 15 μm to 50 μm, more preferably within a rangefrom 20 μm to 50 μm. The particles can be dispersed with desirabledistance from each other when the particle sizes are controlled in therange described above. This makes it possible to secure a path toextract light and improve the directivity while preventing the luminousintensity from decreasing due to the mixing of the filler. When thelight transmitting resin including the fluorescent material and thefiller of particle sizes in the range described above is applied by themimeograph printing, dressing effect can be provided in which the dicingblade is restored from loaded condition in the dicing process aftercuring the light transmitting resin, thus improving the mass productionperformance.

In order to achieve good dressing effect in the dicing process, it ispreferable that the filler of larger particle sizes is included. Gooddressing effect can be achieved for effectively restoring loaded dicingblade when the light transmitting resin includes a filler having medianparticle size within a range from 15 μm to 50 μm, more preferably withina range from 20 μm to 50 μm.

Variation Example 4

(Light Emitting Surface)

According to the present invention, the light transmitting resin surfacethat serves as the light emitting surface of the light emitting diodemay be a curved surface. In the case of the light emitting diodedescribed in the second embodiment in which the resin is molded on thesubstrate, the light transmitting resin surface is preferably formed ina curved surface so as to achieve the desired directivity, since lightcannot be reflected upward on the side wall of the package in this typeof light emitting diode.

Such a curved light emitting surface can be formed by applying the lighttransmitting resin including necessary substances dispersed therein inthe mimeograph printing using a mask 39 (FIG. 7A) having aperturesformed therein in correspondence to the individual light emittingdiodes. This process is illustrated in FIG. 7A and FIG. 7B. While thesurface of the light transmitting resin applied as described aboveusually becomes a curved surface after thermosetting of the resin, thesurface can be formed in any desired shape according to the material andconfiguration of the mask 39. and the quantity of resin applied. Withthis method, the light emitting diode can be manufactured satisfactorilyin mass production. Even when the light emitting diodes of the presentinvention including fluorescent particles of large particle size andfluorescent particles of small particle size are manufactured in a largequantity over a long period of time, variations in the light emissionperformance can be kept extremely small between the light emittingdiodes manufactured in the early stage of the production run and thelight emitting diodes manufactured in the latter stage of the productionrun, thereby improving the yield of production.

Moreover, when silicone is used as the material of the mask 39,producing cost can be reduced and the light emitting surface of adesired curve can be formed by making use of the difference in thethermal expansion coefficient between the silicon and the lighttransmitting resin.

Variation Example 5

While the LED chip and the package are connected by means of wires inthe first embodiment, although the present invention is not limited tothis constitution and such a constitution may also be employed as theLED chip is mounted in the mounting area 1 a of the package by flipchip-bonding with conductive material and output light is extracted fromthe substrate side of the LED chip.

Since the package has the insulating section 4 located in the mountingarea 1 a (through hole) with the thin metal sheets 2 a, 2 b exposed onboth sides as shown in FIG. 1, it suffices to mount the LED chip so asto straddle over the insulating section 4 and connect the positive andnegative electrodes of the LED chip directly to the thin metal sheets 2a, 2 b, respectively.

Variation Example 6

The light emitting diodes of the embodiments and variation examplesdescribed above are SMD type light emitting diodes, although the presentinvention is not limited to this constitution.

For example, the fluorescent material and/or the epoxy resin describedin the first embodiment can be used in light emitting diodes of variousforms such as display, 8-segment indicator and bullet type.

That is, use of the fluorescent material described in the firstembodiment makes it possible to make a light emitting diode of highoutput power and use of the epoxy resin described in the firstembodiment makes it possible to make a light emitting diode of highreliability.

The light transmitting resin described in the first embodiment can beapplied not only to light emitting elements such as light emitting diodebut also to light receiving element such as photodiode.

The present invention will be described in the following examples and isnot limited only to such examples.

EXAMPLE 1

The SMD type light emitting diode as shown in the sectional view of FIG.8 is fabricated as a light emitting diode of the present invention. TheLED chip comprising a light emitting layer made of InGaN and having amain peak of 470 nm is used as a LED chip 5. In the light emitting diodeof Example 1, the package is a molded resin body formed in one piece ofthe base part and the side wall part. The electrode leads 22 a and 22 bare insertion molded into the base part of the resin 24. The LED chipcan be formed by making use of MOCVD method. More specifically, thecleaned sapphire substrate is set in to the reactor chamber and filmsare formed using trimethylgallium (TMG) gas, trimethylindium (TMI) gasand ammonia gas as a reactive gas, and hydrogen gas as a carrier gas,and silane gas and cyclopentadiamagnesium as a impurity gas.

The LED chip comprises a AlGaN layer as a low temperature buffer layer,a non-doped GaN layer to enhance a crystallinity (thickness: about 15000Å), a Si-doped GaN layer as an n-type contact layer on which anelectrode is formed (thickness: about 21650 Å), a non-doped GaN layer toenhance a crystallinity (thickness: about 3000 Å), a multi-layered filmin the form of a super lattice made of a non-doped GaN layer (thickness:about 50 Å) and a Si doped GaN layer (thickness: about 300 Å) as an-type cladding layer, a multi-layered film in the form of a superlattice made of a non-doped GaN layer (thickness: about 40 Å) and anon-doped InGaN layer (thickness: about 20 angstrom) to enhance acrystallinity of the light emitting layer, a light emitting layer in themulti quantum well structure made of a non-doped GaN layer (thickness:about 250 Å) and a non-doped InGaN layer (thickness: about 30 Å), amulti-layered film in the form of a super lattice of a Mg-doped InGaN(thickness: about 25 Å) and a Mg-doped GaAlN (thickness: about 40 Å) anda GaN layer doped with Mg as a p-type contact layer (thickness: about1200 Å), which are sequentially formed, on the sapphire substrate.

The semiconductor wafer on which multiple nitride semiconductor layershave been formed in such a way is etched partially to expose a part ofthe n-type contact layer. Then, on the exposed p-type and n-type contactlayers, the n-type and p-type electrodes are formed, respectively, usingsputtering technique. Thereafter, the resulting wafer is cut into therespective light emitting device to fabricate a LED chip which is ableto emit blue light.

The LED chip fabricated in the above-mentioned way is die-bonded with adie bonding resin 6 to the hollow of the package formed by moldingintegrally the lead electrodes 22 a and 22 b to the resin 24. Eachelectrode of the LED chip and each of the lead electrode 22 a and 22 bare wire-bonded using gold wire 7 having a diameter of 35 μm,respectively, to establish electric connection.

In Example 1 of the present invention, (Y_(0.8)Gd_(0.2)) _(2.965)Al₅O₁₂:Ce_(0.035) in which about 20 percent of Y is substituted with Gd andwhich has a central particle size of 21.429 μm is used as a fluorescentmaterial. The fluorescent material is composed of a fluorescentparticles of large particle size and a fluorescent particles of smallparticle size and has a volume-based particle size distribution as shownin FIGS. 2A and 2B. In the flat range having a slope of zero in thecurve of the volume-based particle size distribution, the cumulativepercentage of particles is 4.6 vol % and the particle size ranges from1.371 μm to 8.379 μm. That is, 4.6 vol % of the whole fluorescentmaterial comprises a fluorescent material of small particle size of aparticle size smaller than 1.371 μm and the remaining 95.6 vol %comprises a fluorescent material of large particle size of a particlesize larger than 8.379 μm. The central particle size of the fluorescentmaterial classified using a settling method to have such a particle sizedistribution is 21.4 μm and the distribution frequency of theabove-mentioned central particle size is 29.12%. The particle size ofpeak of distribution frequency of the fluorescent particles of smallparticle size is 0.613 μm and the particle size of peak of distributionfrequency of the fluorescent particles of large particle size is 22.908μm. A standard deviation in the particle distribution of the fluorescentparticles of large particle size is 0.295.

The fluorescent material, which is adjusted to obtain light of (x,y)=(0.33, 0.33) in a CIE chromaticity diagram and an epoxy resin as alight transmitting resin are mixed at a ratio of 16:100. The resultingepoxy resin containing the fluorescent material is filled by potting inthe hollow of the package in which the LED chip is connected to a pairof lead electrode with gold wire and cured to form a light emittingdiode.

The light emitting diode fabricated in such a manner can emit whitelight of a high intensity and output.

Comparative Example 1

To compare, the light emitting diode having the same chromaticitycoordinates is fabricated in the same way as in Example 1, except that(Y_(0.8)Gd_(0.2)) _(2.965)Al₅O₁₂:Ce_(0.035) fluorescent material havinga wide particle size distribution, of which the curves of volume-basedparticle size distribution are shown in FIGS. 9A and 9B, and a centralparticle size of 6.315 μm is used. The luminus intensity and the outputof the light emitting diode according to Comparative example 1 aredecreased by about 35% and about 25%, respectively, as compared to thelight emitting diode of Example 1. This shows that the light emittingdiode according to the present invention can emit light of highintensity even in the wavelength range where the chromaticity is low,for example, white light.

A standard deviation in the particle size distribution of thefluorescent material which is used in Comparative Example 1 is 0.365.

EXAMPLE 2

The light emitting diode having the same chromaticity coordinates isfabricated in the same way as in Example 1, except that(Y_(0.995)Gd_(0.005)) _(2.750)Al₅O₁₂:Ce_(0.250) fluorescent material isused. This fluorescent material is classified in such a manner that thematerial has a flat range where the cumulative percentage of particlesis 0.077 vol % and the particle size ranges from 1.371 μm to 8.379 μm,the central particle size of the material is 25.626 μm, the distributionfrequency of said central particle size is 24.812%, and peak particlesizes of the distribution frequency of the small particle size and largeparticle size fluorescent particles are 0.613 and 28.012 μm,respectively. The luminous intensity and output of the light emittingdiode of Example 2 is enhanced by about 18% and about 10%, respectively,as compared to the light emitting diode of Example 1. Example 2 canprovide a light emitting diode having a higher intensity light emittingdiode than Example 1.

A standard deviation of the particle size distribution in thefluorescent particles of large particle size is 0.259.

EXAMPLE 3

The light emitting diode having the same chromaticity coordinates isfabricated in the same way as in Example 1, except that the epoxy reinand SiO₂ having a central particle size of 2.5 μm as a diffusing agentwere mixed at the ratio by weight of 100:50 and thereafter, the samefluorescent material as that of Example 1 was mixed into the epoxy resincontaining the diffusing agent. The light emitting diode of Example 3shows the same intensity and output as those of Example 1. The irregularcolor can be inhibited and a good color tone can be achieved, ascompared to Example 1.

EXAMPLE 4

The light emitting diode having the same chromaticity coordinates isfabricated in the same way as in Example 1, except that the lighttransmitting resin containing a fluorescent material was provided usinga mold on the LED chip which was electrically connected to thesubstrate, as shown in FIG. 6. The light emitting diode having a smoothlight emitting plane can be obtained and shows the similar properties tothose of Example 1.

EXAMPLE 5

The light emitting diode having the same chromaticity coordinates isfabricated in the same way as in Example 1, except that the lighttransmitting resin containing a fluorescent material was formed by meansof an intaglio printing method using a mask 39 made of silicone andcured on the substrate to which the LED chip 5 was electricallyconnected, as shown in FIGS. 7A and 7B. The light emitting diode havinga curved light emitting plane can be obtained and shows more even lightemission, as compared to Example 1.

There are provided on the substrate 32 positive electrodes 32 a and 32b, respectively, in correspondence with each LED chip.

EXAMPLE 6

The epoxy resin and SiO₂ having a central particle size of 2.5 μm as adiffusing agent were mixed at the ratio by weight of 100:50 andthereafter, the same fluorescent material as that of Example 2 was mixedinto the epoxy resin containing the diffusing agent. Further, SiO₂having a central particle size of 6 μm as a filler is included at theratio of 70 wt % to the epoxy resin. The resulting material is used as alight transmitting resin. The light transmitting resin was filled in thehollow of the cabinet having a wall on which the LED chip iselectrically connected to a pair of lead electrodes with gold wire usingan intaglio printing method in the same manner as in Example 5. Andthen, the resin was cured at 85° C. for 3 hours and further, at 140° C.for 4 hours to fabricate a light emitting diode having the samechromaticity coordinates as in Example 1. The light emitting diode ofExample 6 has a longer lifetime and emits even light.

EXAMPLE 7

The light emitting diode is fabricated in the same way as in Example 3,except that the fluorescent material similar to that of Example 2 andSiO₂ having a central particle size of about 25 μm which is similar tothat of said fluorescent material, as a filler are used. The luminousintensity of the resulting light emitting diode is increased by 10%, ascompared to that of Example 3.

EXAMPLE 8

The light emitting diode is fabricated in the same way as in Example 6,except that the fluorescent material similar to that of Example 2 andSiO₂ having a roundness which is different by 10% from that of saidfluorescent material and a central particle size of about 25 μm which issimilar to that of said fluorescent material, as a filler are used. Theluminous intensity of the resulting light emitting diode is increased by10%, as compared to that of Example 6.

EXAMPLE 9

As shown in FIG. 10A and FIG. 10B which is a partial enlarged view ofFIG. 10A, the LED chip 5 (similar to that of Example 1) is die-bondedwith epoxy resin 42 to the cup portion of the mount lead 42 a made ofbright plated copper and thereafter, each electrode of the LED chip 5and the mount lead 42 a and the second lead 42 b are wire-bonded,respectively, using a wire 7 having a diameter of 30 μm. The mixture ofthe fluorescent material similar to that of Example 2, which is adjustedto obtain light of (x, y)=(0.33, 0.33) in a CIE chromaticity diagram andan epoxy resin as a light transmitting resin at a ratio by weight of5:100 is filled in the cup of said mount lead and then, cured at 150° C.for 1 hour to form a coating part containing a fluorescent material.Further, a cannonball type lens 49 is formed using the transparent epoxyresin, so as to obtain a round shape in view of light emittingobservation plane. The resulting lamp type light emitting diode haseffects similar to those of Example 1.

EXAMPLE 10

The lamp type light emitting diode is fabricated in the same way as inExample 9, except that the fluorescent material similar to that ofExample 2, the epoxy resin which is a light transmitting resin and SiO₂having a roundness which is different by 10% from that of saidfluorescent material and a central particle size of about 25 μm as afiller are mixed at a ratio by weight of 100:10:35 and the resultingmixture is filled in the cup of the mount lead. Brighter and more evenlight is emitted, as compared to Example 9.

EXAMPLE 11

The LED chip similar to that of Example 1 is placed in the hollow of theresin package into which the lead electrode is inserted. The siliconeresin which is a light transmitting resin, the fluorescent materialsimilar to that of Example 1, the fluorescent material composedY_(2.965)Al₅O₁₂:Ce_(0.035) having a central particle size of 13 μm andSiO₂ having a central particle size of about 0.5 μm are mixed at a ratioby weight of 100:0.69:0.5:10 and the resulting mixing solution is filledin said hollow, so as to fabricate a light emitting diode. The resultinglight emitting diode has effects similar to those of Example 1, a goodcolor rendering and a high brightness.

EXAMPLE 12

The light emitting diode is fabricated in the same way as in Example 11,except that the silicone resin which is a light transmitting resin,(Y_(0.9)Gd_(0.1))_(2.965)Al₅O₁₂:Ce_(0.035) having a central particlesize of 30 μm, the fluorescent material similar to that of Example 2,and SiO₂ having a central particle size of about 0.5 μm are mixed at aratio by weight of 100:0.69:0.5:10 and the resulting mixing solution isfilled in said hollow. The resulting light emitting diode has effectssimilar to those of Example 2, a good color rendering and a highbrightness.

EXAMPLE 13

Example 13 is an example of a producing method according to the firstembodiment.

In Example 13, the surface-mounted type of light emitting diode as shownin FIG. 1 is fabricated.

In Example 13, the LED chip 5 is a nitride semiconductor LED chipcomprising a light emitting layer made of In_(0.2)Ga_(0.8)N which has amonochromic light emitting peak of 475 nm in the visible region. Morespecifically, the LED chip 5 is fabricated by forming nitridesemiconductor layers on the cleaned sapphire substrate using a TMG(trimethylgallium) gas, a TMI (trimethylindium) gas, a nitrogen gas anda dopant gas with a carrier gas, by means of MOCVD method. In this case,the n-type nitride semiconductor and p-type nitride semiconductor layersare formed, respectively, by using SiH₄ and Cp₂Mg as a dopant gas.

The LED chip 5 comprises a buffer layer made of GaN which is grown at alow temperature, an n-type GaN layer which is an undoped nitridesemiconductor, a Si-doped GaN layer (n-type contact layer) on which ann-electrode is formed, a light emitting layer in the multi quantum wellstructure in which one group consisting of the GaN layer as a barrierlayer, the InGaN layer as an well layer and the GaN layer as a barrierlayer is sandwiched between the GaN layers, a Mg-doped AlGaN layer(p-type cladding layer),and a Mg-doped GaN layer (p-type contact layer),which are sequentially formed, on the sapphire substrate.

The p-type semiconductor is annealed at the temperature of 400° C. ormore after forming layers.

After forming layers, each of p-type and n-type contact layers isexposed by etching on the same surface side of the nitride semiconductoron the sapphire substrate. The positive and negative electrodes areformed on each contact layer, respectively, by sputtering. The metalthin film is formed as a translucent electrode on the entire surface ofthe p-type nitride semiconductor and thereafter, the basic electrode isformed on a part of the translucent electrode. The resulting wafer isscribed and cut by eternal forces into LED chips which are lightemitting devices.

The LED chip fabricated in the above-mentioned way is die-bonded with anepoxy resin into each via hole of the package assembly which has beendescribed in the first embodiment. Each electrode of the LED chip iselectrically connected to the metal films 2 a and 2 b, respectively bywire bonding using gold wire.

The fluorescent material is fabricated as follow.

Rare earth elements, Y, Gd and Ce, are dissolved in an acid at a ratioof stoichiometry and the resulting solution is coprecipitated withoxalic acid. The resulting coprecipitate is calcined and the obtainedoxide of coprecipitate and aluminum oxide are mixed. The resultingmixture as a flux is mixed with barium fluoride and filled into thecrucible and then, heated at 1400° C. for 3 hours in the air to obtain aburned product. The burned product is ground in water with a ball milland washed, separated, dried and then, at last, combed to form(Y_(0.995)Gd_(0.005))_(2.750)Al₅O₁₂:Ce_(0.250) fluorescent material.

An alicyclic epoxy resin composite (viscosity 8000 mPa·s) obtained bymixing and dispersing 17 wt % of said fluorescent material and 70 wt %of SiO₂ having a central particle size of 10 μm into the epoxy resincontaining 20 wt % of SiO₂ having a central particle size of 0.3 μm isused as a material for sealing members.

In this Example 13, the mask 112 made of stainless steel and having athickness of 100 μm is used. The mask design is the same as in FIG. 3that is described in the first embodiment. The package assembly on whichthe LED chip is located is inhaled to the mask 112 with the stage forelevating the substrate mounted in such a way that the opening side ofthe via hole is aimed at the mask 112, to make contact with the mask112.

Said light transmitting resin is applied to the end of the mask 112 in apredetermined amount required for printing and the pressure is reducedto 330 Pa. After the completion of decompression, an air pressure of0.10 Mpa is applied to the knife 14 inclined at 30° in the operatingdirection with respect to the perpendicular line of the mask 112 to runthe squeegee in one direction. Next, the inside of the chamber ispressurized to 20000 Pa. After completion of compression, an airpressure of 0.12 Mpa is applied to the knife 15 inclined at 35° in thedirection opposite to said squeegee with respect to the perpendicularline of the mask 112 to run the squeegee in the other direction. Thisreciprocating squeegee is repeated twice.

Next, the stage for elevating the substrate is lowered to separate thepackage assembly from the mask 112. Then, the light transmitting resinis primarily cured at 85° C. for 3 hours and secondarily cured at 140°C. for 4 hours. In this way, the light transmitting resin having ansmooth surface is formed over the via hole and the insulating substrateon either side thereof.

Next, to the ultraviolet radiation cured dicing adhesive sheet having athickness of 150 μm and comprising an adhesive layer of 20 μm inthickness is attached the package assembly with the light transmittingresin side of the assembly opposite to the adhesive layer. The packageassembly and the dicing adhesive sheet are cut into the depth of 100 μmusing a dicing blade from the bottom of the package assembly to cut awayrespective light emitting diodes. Finally, the ultraviolet radiation isapplied to the package assembly from the film side to cure the adhesivelayer and then the assembly is cut away into each light emitting diode.When 500 of the surface-mounted diode type (SMD type) light emittingdiodes obtained in this way were tested for variations, it has beenshown that variations in chromaticity are small among different lightemitting diodes and that visually, there is no unevenness in emittedlight in each light emitting diode.

Comparative Example

The light emitting diode is fabricated in the same way as in Example 13,except that the mask formed in such a way that one opening correspondsto one via hole of the package assembly is used. The light transmittingresin filled in the top surface of the resulting light emitting diodeleaks on the top surface of substrate on each side. The resulting lightemitting diode is adhered to the adhesive sheet for dicing and cut away,each light emitting diode comes apart.

When 500 of the resulting light emitting diodes are observed, there areburrs on the top surface, as compared to Example 1. Where 500 of lightemitting diodes were implemented, variations in color temperature duringproducing were examined. Variations in color temperature duringproducing for the light emitting diodes of Example 13 were reduced byabout 20%, as compared to the area on the chromaticity diagram for thelight emitting diodes of Comparative example.

EXAMPLE 14

The surface-mounted light emitting diode is fabricated in the same wayas in Example 13, except that an alicyclic epoxy resin composite(viscosity: 15000 mPa·s) obtained by mixing and dispersing 15 wt % ofthe above-mentioned fluorescent material and 40 wt % of SiO₂ having acentral particle size of 10 μm into the undoped one-liquid-cured epoxyresin including a bridged oligomer is used as a material for a sealingmember. The luminous intensity and output are increased, as compared toExample 13. Moreover, the reliability can be improved dramatically.

In Example 15, (Y_(0.8)Gd_(0.2))_(2.965)Al₅Gd₁₂:Ce_(0.035) in whichabout 20 percent of Y is substituted with Gd and which has a centralparticle size of 21.429 μm is prepared in the same way as in Example 13.The fluorescent material is composed of a fluorescent material of largeparticle size and a fluorescent material of small particle size. In theflat range having a slope of zero in the curve of the volume-basedparticle size distribution, the cumulative percentage of particles is4.6 vol % and the particle size ranges from 1.371 μm to 8.379 μm. Thatis, 4.6 vol % of the whole fluorescent material comprises fluorescentparticles of small particle size smaller than 1.371 μm and the remaining95.6 vol % comprises fluorescent particles of large particle size largerthan 8.379 μm. The central particle size of the fluorescent materialclassified using a settling method to have such a particle sizedistribution is 21.4 μm and the frequency of the above-mentioned centralparticle size is 29.12%. The particle size of peak of distributionfrequency of the fluorescent particles of small particle size is 0.613μm and the particle size of peak of distribution frequency of thefluorescent particles of large particle size is 22.908 μm. Where thefluorescent material having such a particle size distribution is used,the luminous intensity and light emitting output can be enhanced.

In example 15, the surface-mounted type light emitting diode isfabricated in the same way as in Example 14, except that 15 wt % of theabove-mentioned fluorescent material is added to the resin composite.The light emitting diode of Example 15 can achieve an effect similar tothat of Example 14. The brightness of the light emitting diode ofExample 15 is higher than that of Example 14.

EXAMPLE 16

Four kinds of resins C, D, E and F, which were epoxy resins according tothe present invention, and the resins A and B of Comparative examplewere prepared and the characteristics thereof were examined.

1. Preparation of the Epoxy Resin Composite

The epoxy resin composites A to F were prepared under the followingconditions. Where acid anhydride was added, the conversion ratio of acarboxyl group to an ester group was estimated. The ester conversionratio is the ratio, expressed as a molar percentage, of the carboxylgroups included in the acid anhydride, which have been converted intoester groups. The ester conversion ratio was examined using aneutralization reaction with KOH solution. Specifically, 1.00 g of theepoxy resin was dissolved in 50 mL of ethanol and 0.1 N KOH solution inwater was added. At the point of neutralization, the color of the BTBindicator turned from yellow into blue (at pH 7.6). The amount ofcarboxyl groups which were not converted into ester groups wasdetermined using the mount of KOH solution in water required forneutralization.

Resin A: Comparative Example

256 g (1.95e.eq)g of 3′4′-epoxy-cyclohexylmethyl3,4-epoxy-cyclohexanecarboxylate, which is a derivative of cyclohexeneepoxidated compound as an alicyclic epoxy resin and 0.6 g of Benzylp-hydroxyphenyl methylsulfonium Hexafluoroantimonate, which is anaromatic sulfonium salt (anion species is hexafluoroantimony) and abenzylsulfonium-based catalyst, as a cationic curing agent, were put inthe 300 mL four neck flask. The resulting mixture was stirred for 0.5hour and heated at 85° C. for 3 hours and further at 140° C. for 4 hoursto be cured.

Resin B: Comparative Example

7.68 g of propylene glycol monoglycidyl ether is added (3 wt % withrespect to the epoxy resin) as a reactive diluent was added to thecomponent of resin A. The resulting mixture was stirred for 0.5 hour andheated at 85° C. for 3 hours and further at 140° C. for 4 hours to becured.

Resin C: Present Invention

256 g (1.95e.eq) of 3′4′-epoxy-cyclohexylmethyl3,4-epoxy-cyclohexanecarboxylate as an alicyclic epoxy resin, 104.29 g(6.09×10⁻¹ mol) of the mixture of 4-methylhexahydrophthalicanhydrate/hexahydrophthalic anhydrate at a ratio of 70/30, 2.56 g(4.12×10⁻² mol) of ethylene glycol as a promoter and 0.6 g of Benzylp-hydroxyphenyl methylsulfonium Hexafluoroantimonate, which is abenzylsulfonium-based catalyst, as a cationic curing agent, were put inthe 300 mL four neck flask. The resulting mixture was stirred for 0.5hour and the ester conversion ratio was measured to be 0%. Aftermeasurement, the mixture was heated at 85° C. for 3 hours and further at140° C. for 4 hours to be cured.

Resin D: Present Invention

256 (1.95e.eq) g of 3′4′-epoxy-cyclohexylmethyl3,4-epoxy-cyclohexanecarboxylate as an alicyclic epoxy resin, 9.57 g(5.69×10⁻² mol) of the mixture of 4-methylhexahydrophthalicanhydrate/hexahydrophthalic anhydrate at a ratio of 70/30 and 1.77 g(2.85×10⁻² mol) of ethylene glycol as a promoter were put in the 300 mLfour neck flask and the temperature was increased slowly with amultiheater and maintained at 90 to 100° C. for 16 hours. Thetemperature was decreased slowly to room temperature. Then, 0.6 g ofBenzyl p-hydroxyphenyl methylsulfonium Hexafluoroantimonate, which is abenzylsulfonium-based catalyst, as a cationic curing agent, was added.The resulting mixture was stirred for 0.5 hour and the conversion ratioof the carboxyl group into the ester group was measured to be 90.6%.After measurement, the mixture was heated at 85° C. for 3 hours andfurther at 140° C. for 4 hours to be cured.

Resin E: Present Invention

The epoxy resin composite was prepared in the same way as resin D,except that 256 g (1.95e.eq) of 3′4′-epoxy-cyclohexylmethyl3,4-epoxy-cyclohexanecarboxylate as an alicyclic epoxy resin, 15.95 g(9.48×10⁻² mol) of the mixture of 4-methylhexahydrophthalicanhydrate/hexahydrophthalic anhydrate at a ratio of 70/30, 2.95 g(4.75×10⁻² mol) of ethylene glycol as a promoter and 0.6 g of Benzylp-hydroxyphenyl methylsulfonium Hexafluoroantimonate, which is abenzylsulfonium-based catalyst, as a cationic curing agent, were used.The ester conversion ratio of the carboxyl group into the ester groupwas measured to be 94.2%.

Resin F: Present Invention

The epoxy resin composite was prepared in the same way as resin D,except that 256 g (1.95e.eq) of 3′4′-epoxy-cyclohexylmethyl3,4-epoxy-cyclohexanecarboxylate as an alicyclic epoxy resin, 25.52 g(1.52×10⁻¹ mol) of the mixture of 4-methylhexahydrophthalicanhydrate/hexahydrophthalic anhydrate at a ratio of 70/30, 4.72 g(7.60×10⁻² mol) of ethylene glycol as a promoter and 0.6 g of Benzylp-hydroxyphenyl methylsulfonium Hexafluoroantimonate, which is abenzylsulfonium-based catalyst, as a cationic curing agent, were used.The ester conversion ratio of the carboxyl group into the ester groupwas measured to be 92.4%.

2. Flexibility Examination

The light emitting diode as shown in FIG. 1 was fabricated using theepoxy resin composites A to F and the impact test in liquid phase wascarried out to evaluate flexibility of the resin.

No fluorescent material was mixed into the epoxy resin composite of thelight emitting diode used for this examination.

In this impact test in liquid phase, the cycle consisting of dipping inthe liquid phase of −40° C. for one minute and dipping in the liquidphase of 100° C. for one minute was repeated 500 to 2500 cycles andthen, the number of the occurrence of cracks into the LED chip or ofmalfunction due to wire open was examined (test samples: 100).

The examination results are shown in table 1. For the resin A obtainedby curing the alicyclic epoxy resin only with a cationic curing agent,the malfunction due to cracks occurred since the initial stage of thetest and the ratio of malfunction reached 100% after 1000 cycles. Forthe resin B of which the flexibility was enhanced by adding a reactivediluent, 7% of malfunction occurred after 2500 cycles. On the otherhand, for any resins C, D, E and F according to the present invention,the ratio of the occurrence of malfunction was not more than 4% after2500 cycles. Particularly, for the resins D, E and F in which theconversion into ester was advanced, the occurrence ratio of malfunctionwas 0%. It was confirmed that he epoxy resin composite of the presentinvention has a more excellent flexibility than that of the conventionalepoxy resin of which the flexibility is enhanced using a reactivediluent.

TABLE 1 Occurrence ratio of malfunction 500 1000 1500 2000 2500 Cause ofcycle cycle cycle cycle cycle malfunction Resin A: 39% 100% 100% 100%100% crack Comparative example Resin B: 0% 0% 1% 4% 7% crack Comparativeexample Resin C: example 1% 1% 3% 3% 4% crack Resin D: example 0% 0% 0%0% 0% — Resin E: example 0% 0% 0% 0% 0% — Resin F: example 0% 0% 0% 0%0% —3. Light Resistance (Yellowing) Examination

The light resistance test was carried out using the epoxy resins B andF. The test piece of 30×30×3 mm was fabricated and radiated with a xenonlamp for 100 hours at 120° C. to examine the change in overalltransmittance of beam before and after the radiation. The transmittancewas measured with a spectroscopic calorimeter (made by Murakami ColorLab.). The examination results are shown in FIGS. 11A and 11B. FIG. 11Ashows the overall transmittance of beam before radiation and FIG. 11Bshows the overall transmittance of beam after radiation. For the resinB, a conventional epoxy resin composite to which a reactive diluent wasadded, the transmittance in the range of a short wavelength decreasedand the color was changed into yellow in the early stage. Thetransmittance further decreased in the range of a short wavelength andthe yellowing was advanced remarkably during the light resistance test.

On the other hand, for the resin F, an epoxy resin composite of thepresent invention, no coloring was observed in the early stage and afterthe light resistance test.

4. Heat Resistance Examination

The heat resistance test was carried out using the epoxy resins A, B andF. The test piece of 30×30×3 mm was fabricated and heated at 120° C. for500 hours in an oven to examine the change in overall transmittance ofbeam before and after the heating. The transmittance was measured with aspectroscopic calorimeter (made by Murakami Color Lab.). The examinationresults are shown in FIGS. 12A and 12B. FIG. 12A shows the overalltransmittance of beam before heating and FIG. 12B shows the overalltransmittance of beam after heating.

The resin A, a conventional epoxy resin composite to which a cationiccuring agent was added, showed a transmittance similar to that of theresin F, an epoxy resin composite of the present invention, in the earlystage. But for the resin A, the transmittance in the range of a shortwavelength decreased and the color was changed into yellow during theheat resistance test.

For the resin B, a conventional epoxy resin composite to which areactive diluent was added, the transmittance in the range of a shortwavelength decreased and the color was changed into yellow in the earlystage. The transmittance further decreased in the range of a shortwavelength and the yellowing was advanced remarkably during the lightresistance test.

On the other hand, for the resin F, an epoxy resin composite of thepresent invention, no coloring was observed in the early stage and theyellowing was advanced during the heat resistance test, but the heatresistance was better than that of resin B.

5. LED Current Passed Life Examination

The light emitting diode having a structure as shown in FIG. 1 wasfabricated using epoxy resin composites B and F and the current passedlife test (current: 10 mA) was carried out at room temperature (25° C.)and at an elevated temperature and a high humidity(85° C., 85%). FIGS.13 and 14 are graphs showing changes in relative outputs P₀% (therelative value of outputs where the output in the early stage is 100%)of LED during the current passed life test at room temperature and at anelevated temperature and a high humidity, respectively. As shown inFIGS. 13 and 14, for the epoxy resin composite of the present invention,the reduction of the LED output during life was smaller than that of theconventional epoxy resin composite B.

6. Pot Life Examination

The change in viscosity over time was examined at 50° C. using the epoxyresin composites B and F. The examination results are shown in FIG. 15.The conventional epoxy resin composite B had a pot life of about 25hours, while the epoxy resin composite of the present invention F had apot life of about 40 hours.

EXAMPLE 17

The surface-mounted type light emitting diode as shown in FIG. 1 wasfabricated. In this light emitting diode of Example 17, a fluorescentmaterial was mixed with the light transmitting resin. The LED chip 5comprises a nitride semiconductor device including a light emittinglayer made of In_(0.2)Ga_(0.8)N semiconductor having a monochromicemission peak of 475 nm in the visible range. That is, the same LED chipas that of Example 13 was used.

The package used was also the same as that of Example 13.

The fluorescent material used was also the same as that of Example 13.

To the above-mentioned resin F, 15 wt % of said fluorescent material and40 wt % of SiO₂ having a central particle size of 10 μm were mixed anddispersed to obtain an alicyclic epoxy resin composite (viscosity: 15000mPa·s) as a light transmitting resin.

500 light emitting diodes were fabricated in the same way as in Example13.

The variations among 500 light emitting diodes fabricated in this waywere examined. It was shown that variations in chromaticity among thelight emitting diodes were small and there was no visual emissionunevenness in each light emitting diode. The reliability could beenhanced extremely, as compared to the diode using the resin A.

Comparative Example

The light emitting diode was fabricated in the same way as in Example17, except that the resin A and the mask having an opening correspondingto one via hole in the insulating substrate were used. The emissionunevenness was observed and the even emission could not be achieved. Thereliability decreased, as compared to Example 17.

EXAMPLE 18

The light emitting diode was fabricated in the same way as in Example17, except that the same fluorescent material as that of Example 15 wasused and 15 wt % of the fluorescent material was included into the resinF. The light emitting diode of Example 18 showed effects similar tothose of Example 1 and had a higher brightness than that in Example 17.

The following examples will describe the synthesis of the fluorescentmaterial.

EXAMPLE 19 The Synthesis of the Fluorescent Material by Means of aTwo-step Calcination Method in Reducing Atmospheres

The following examples relate to the method of the fluorescent materialsuited for the light emitting diode.

According to the method of Example 19, a flux is mixed into the mixturematerial which has been adjusted to achieve the composition of thefluorescent material and the resulting mixed is filled in the crucibleand calcined at 1400° C. to 1600° C. for 6 to 8 hours in the weaklyreducing atmosphere and further, at 1400° C. to 1600° C. for 6 to 8hours in the reducing atmosphere. The resulting calcination product isground and passed through a comb of 200 mesh to form a fluorescentmaterial.

In this way, the mixture consisting of the mixed raw material and theflux is calcined using a two-step calcination method comprising thefirst calcination step in the weakly reducing atmosphere and the secondcalcination step in the reducing atmosphere, so as to obtain afluorescent material having a high absorbing efficiency of theexcitation wavelength. Therefore, where the resulting fluorescentmaterial is applied to the light emitting diode as shown in FIG. 1, theamount of the fluorescent material required to obtain the desired tonecan be reduced and the light emitting diode having a high efficiency oflight extraction can be achieved.

EXAMPLE 20 Oxides of Each Raw Material are Mixed at a StoichiometricRatio. Flux:Aluminum Fluoride

First, the mixture material is obtained by mixing Y₂O₃, Gd₂O₃, Al₂O₃ andCeO₂ at a stoichiometric ratio. To the resulting mixture material,aluminum fluoride is added as a flux and mixed with a ball mill mixerfor 2 hours. Next, after removing the ball, the resulting mixture isfired at 1400 to 1600° C. for 6 to 8 hours in a weakly reducingatmosphere and further at 1400 to 1600° C. for 6 to 8 hours in areducing atmosphere. The resulting firing product is ground and passedthrough a comb of 200 mesh to form a fluorescent material. Where theresulting fluorescent material is irradiated with an exciting light inthe blue range, the fluorescent material emits light of (x, y)=(0.457,0.527) in chromaticity coordinates (JISZ8110). For example, where thisfluorescent material is used for the light emitting diode as shown inFIG. 1, the similar results to those of Example 19 can be achieved.

EXAMPLE 21 Barium Fluoride+Boric Acid is used as a Flux in Example 20

First, the mixture material is obtained by mixing Y₂O₃, Gd₂O₃, Al₂O₃ andCeO₂ at a stoichiometric ratio. To the resulting mixture material,barium fluoride+boric acid is added as a flux and mixed with a ball millmixer for 2 hours. Next, after removing the ball, the resulting mixtureis calcined at 1400 to 1600° C. for 6 to 8 hours in a weakly reducingatmosphere and further at 1400 to 1600° C. for 6 to 8 hours in areducing atmosphere. The resulting calcination product is ground andpassed through a comb of 200 mesh to form a fluorescent material. Wherethe resulting fluorescent material is irradiated with an exciting lightin the blue range, the fluorescent material emits light of (x,y)=(0.454, 0.531) in chromaticity coordinates (JISZ8110).

The fluorescent material formed using barium fluoride as a flux has alonger y value of chromaticity and a smaller amount of red component, acompared to the material using other substances as a flux.

For example, where this fluorescent material is used for the lightemitting diode as shown in FIG. 1, the similar results to those ofExample 19 can be achieved.

EXAMPLE 22 10 wt % of a Liquid is Added During Calcination in Example 21

First, the mixture material is obtained by mixing Y₂O₃, Gd₂O₃, Al₂O₃ andCeO₂ at a stoichiometric ratio. To the resulting mixture material,barium fluoride+boric acid is added as a flux and mixed with a ball millmixer for 2 hours. Next, after removing the ball, 10 wt % of a liquidsuch as pure water with respect to the resulting powder is added and theresulting mixture is calcined at 1400 to 1600° C. for 6 to 8 hours in aweakly reducing atmosphere and further at 1400 to 1600° C. for 6 to 8hours in a reducing atmosphere. The resulting calcination product isground and passed through a comb of 200 mesh to form a fluorescentmaterial. Where the resulting fluorescent material is irradiated with anexciting light in the blue range, the fluorescent material emits lightof (x, y)=(0.455, 0.530) in chromaticity coordinates (JISZ8110).

For example, where this fluorescent material is used for the lightemitting diode as shown in FIG. 1, the similar results to those ofExample 19 can be achieved.

EXAMPLE 23 37.5 wt % of a Liquid is added During Calcination in Example21

First, the mixture material is obtained by mixing Y₂O₃, Gd₂O₃, Al₂O₃ andCeO₂ at a stoichiometric ratio. To the resulting mixture material,barium fluoride+boric acid is added as a flux and mixed with a ball millmixer for 2 hours. Next, after removing the ball, 37.5 wt % of a liquidsuch as pure water with respect to the resulting powder is added and theresulting mixture is calcined at 1400 to 1600° C. for 6 to 8 hours in aweakly reducing atmosphere and further at 1400 to 1600° C. for 6 to 8hours in a reducing atmosphere. The resulting calcination product isground and passed through a comb of 200 mesh to form a fluorescentmaterial. Where the resulting fluorescent material is irradiated with anexciting light in the blue range, the fluorescent material emits lightof (x, y)=(0.458, 0.528) in chromaticity coordinates (JISZ8110).

For example, where this fluorescent material is used for the lightemitting diode as shown in FIG. 1, the similar results to those ofExample 19 can be achieved.

EXAMPLE 24 62 wt % of a Liquid is Added During Calcination in Example 21

First, the mixture material is obtained by mixing Y₂O₃, Gd₂O₃, Al₂O₃ andCeO₂ at a stoichiometric ratio. To the resulting mixture material,barium fluoride+boric acid is added as a flux and mixed with a ball millmixer for 2 hours. Next, after removing the ball, 62 wt % of a liquidsuch as pure water with respect to the resulting powder is added and theresulting mixture is calcined at 1400 to 1600° C. for 6 to 8 hours in aweakly reducing atmosphere and further at 1400 to 1600° C. for 6 to 8hours in a reducing atmosphere. The resulting calcination product isground and passed through a comb of 200 mesh to form a fluorescentmaterial. Where the resulting fluorescent material is irradiated with anexciting light in the blue range, the fluorescent material emits lightof (x, y)=(0.461, 0.526) in chromaticity coordinates (JISZ8110).

For example, where this fluorescent material is used for the lightemitting diode as shown in FIG. 1, the similar results to those ofExample 19 can be achieved.

Industrial Applicability

The present invention can provide the light emitting diode having a lessirregular color, good reliability, good productivity, and high utilityvalue.

1. An epoxy resin composition comprising: an epoxy resin comprising analicyclic epoxy resin in an amount of 65% by weight or more of the epoxyresin, an acid anhydride represented by the general formula (1) ordicarboxylic acid represented by the general formula (2) in an amount of0.005 to 1.5 mol based on an epoxy equivalent of the epoxy resin, and acation curing agent in an amount of 0.0001 to 0.01 mol based on an epoxyequivalent of said epoxy resin

wherein R₁ represents a cyclic or aliphatic alkyl, or a cyclic oraliphatic aryl, said R₁ having 0 to 12 carbon atoms and R₂ represents analkyl or aryl, said R₂ having 0 to 12 carbon atoms.
 2. The epoxy resincomposition according to claim 1: wherein said alicyclic epoxy resin isa resin selected from the group consisting of an epoxidated cyclohexenederivative, a hydrated bisphenol A diglycidyl ether and a diglycidylhexahydrophthalate ester.
 3. The epoxy resin composition according toclaim 1: wherein said cation curing agent is one selected from the groupconsisting of an aromatic sulfonium salt, an aromatic diazonium salt, anaromatic iodonium salt and an aromatic selenium salt.
 4. The epoxy resincomposition according to claim 1 further comprising: a polyhydricalcohol or a polycondensate thereof in the amount of 0.1 to 5.0equivalents based on the acid anhydride or dicarboxylic acid.
 5. Theepoxy resin composition according to claim 4: wherein said polyhydricalcohol is one selected from the group consisting of an ethylene glycol,a diethylene glycol, a trimethylene glycol, a triethylene glycol, apropylene glycol, a 1,4-butanediol, and a 1,6-hexanediol.
 6. A methodfor producing the epoxy resin composition according to claim 1comprising: reacting said epoxy resin and said acid anhydride ordicarboxylic acid to obtain a crosslinked oligomer, mixing of said crosslinked oligomer and said cation curing agent.
 7. An opticalsemiconductor device comprising: at least a pair of lead electrodes, anoptical semiconductor chip that is electrically connected to said leadelectrodes, and a molding resin that seals said optical semiconductorchip, wherein the molding resin comprises said epoxy resin compositionaccording to claim
 1. 8. The optical semiconductor device according toclaim 7, wherein said optical semiconductor chip is mounted on a surfaceof a substrate having said lead electrodes formed thereon.
 9. Theoptical semiconductor device according to claim 7: wherein said opticalsemiconductor chip is a light emitting diode chip having a lightemitting layer made of a nitride semiconductor that includes at least inand Ga and a main peak of emission at a wavelength of 550 nm or shorter.